Systems/methods of transmitting information via baseband waveforms comprising agility in frequency content and an orthogonality therebetween

ABSTRACT

Communications systems and/or methods are disclosed that may be used to convey information by forming, and then using, a plurality of frequency agile baseband waveforms, wherein any two different waveforms of the plurality of frequency agile baseband waveforms comprise an orthogonality therebetween. The systems/methods disclosed can convey information by mapping an information sequence into a baseband waveform sequence that includes waveforms of the plurality of baseband waveforms, and by transmitting the baseband waveform sequence. Such systems and/or methods can provide extreme privacy, cognitive radio capability, robustness to fading and interference, communications performance associated with M-ary orthonormal signaling and/or high multiple-access capacity.

CLAIM FOR PRIORITY

This application is a continuation of U.S. patent application Ser. No.14/187,899, filed Feb. 24, 2014, entitled Systems and/or Methods ofWireless Communications, which itself is a continuation of U.S. patentapplication Ser. No. 13/011,451, filed Jan. 21, 2011, entitled Systemsand/or Methods of Increased Privacy Wireless Communications, whichitself is a continuation-in-part of U.S. patent application Ser. No.12/372,354, filed Feb. 17, 2009, entitled Wireless CommunicationsSystems and/or Methods Providing Low Interference, High Privacy and/orCognitive Flexibility, which itself claims priority to U.S. ProvisionalApplication No. 61/033,114, filed Mar. 3, 2008, entitled Next Generation(XG) Chipless Spread-Spectrum Communications (CSSC), and is acontinuation-in-part (CIP) of U.S. application Ser. No. 11/720, 115,filed May 24, 2007, entitled Systems, Methods, Devices and/or ComputerProgram Products For Providing Communications Devoid of CyclostationaryFeatures, which is a 35 U.S.C. §371 national stage application of PCTApplication No. PCT/US2006/020417, filed on May 25, 2006, which claimspriority to U.S. Provisional Patent Application No. 60/692,932, filedJun. 22, 2005, entitled Communications Systems, Methods, Devices andComputer Program Products for Low Probability of Intercept (LPI), LowProbability of Detection (LPD) and/or Low Probability of Exploitation(LPE) of Communications Information, and also claims priority to U.S.Provisional Patent Application No. 60/698,247, filed Jul. 11, 2005,entitled Additional Communications Systems, Methods, Devices andComputer Program Products for Low Probability of Intercept (LPI), LowProbability of Detection (LPD) and/or Low Probability of Exploitation(LPE) of Communications Information and/or Minimum InterferenceCommunications, the entirety of all of which are incorporated herein byreference. The above-referenced PCT International Application waspublished in the English language as International Publication No. WO2007/001707.

FIELD OF THE INVENTION

This invention relates to low interference, high privacy, featurelesscovert communications systems and/or methods that may also comprisecognitive capability. More specifically, the invention relates towireless communications systems and/or methods (that may comprisewireless spread-spectrum communications systems and/or methods), thatcan provide low interference, high privacy, high covertness, featurelessand/or cognitive capability. The invention also relates to LowProbability of Intercept (LPI), Low Probability of Detection (LPD), LowProbability of Exploitation (LPE) and/or Minimum InterferenceCommunications (MIC) systems, methods, devices and/or computer programproducts that may also be used to provide low interference, white spacespectrum communications commercially.

BACKGROUND

In wireless communications, access to sufficient spectrum is becomingincreasingly difficult owing to an ever-increasing desire of users forfaster multi-media broadband services. Known systems and/or methods ofLPI/LPD/LPE and/or Jam Resistant (JR) communications and/or BurstCommunications (BURSTCOMM) may combine, in general, hybridspread-spectrum waveforms comprising Frequency-Hopping (FH), DirectSequence Pseudo-Noise (DSPN) spreading and/or Time-Hopping (TH) toincrease covertness and/or resistance to jamming. Transmitting a FH/DSPNspread-spectrum waveform in pseudo-random short bursts using, forexample, a TH technique, may, for example, reduce an interceptor'sability to integrate sufficient energy to trigger a detectabilitythreshold associated with a radiometer that the interceptor may be usingas a means of signal detection/identification. It is known that aradiometric approach to signal detection/identification may yield asuboptimum and/or unsatisfactory performance measure when attempting todetect/identify/exploit a FH/DSPN/TH spread-spectrum communicationssignal in a changing noise and/or interference environment. This may bedue to a background noise/interference level and/or a signal energyreaching the interceptor's receiver being insufficient over theinterceptor's radiometric integration time.

SUMMARY

A wireless communications system configured for Low Probability ofIntercept (LPI), Low Probability of Detection (LPD) and/or LowProbability of Exploitation (LPE) communications may use waveformssubstantially devoid of a cyclostationary signature to improve aLPI/LPD/LPE property. A set of M independent “seed” waveforms thatsatisfy a time-bandwidth constraint may be used via a Gram-SchmidtOrthogonalization (GSO) procedure to generate M orthonormal functions.In accordance with exemplary embodiments of the present invention, the Mseed waveforms may, for example, be chosen from a band-limitedGaussian-distributed process (such as, for example, Gaussian-distributedpseudo-random noise) and may be used to generate, via anorthogonalization operation, such as, for example, a GSO, acorresponding set of M Gaussian-distributed orthonormal functionssubstantially devoid of a cyclostationary property.

The set of M Gaussian-distributed orthonormal functions may be used in acommunications system to define a signaling alphabet of a transmitter ofthe communications system (and a corresponding matched filter bank of areceiver of the communications system) to thereby reduce or eliminate acyclostationary signature of a transmitted communications waveform andthus increase a covertness measure and/or a privacy measure of thecommunications system.

The set of M Gaussian-distributed orthonormal functions may be updated,modified and/or changed as often as necessary to further increase and/ormaximize a covertness/privacy measure of the communications system.

A receiver of the communications system may be equipped withsubstantially the same algorithm(s) that are used by the transmitter ofthe communications system and the receiver may be substantiallysynchronized with the transmitter to thereby re-create and use at thereceiver the M Gaussian-distributed orthonormal functions for detectionof communications information.

The set of M orthonormal functions may, in some embodiments, be a set oforthogonal but not necessarily orthonormal functions. In furtherembodiments, the set of M orthonormal functions may be non-Gaussiandistributed and may be, for example, uniformly distributed, Rayleighdistributed and/or distributed in accordance with any other known(continuous and/or discrete) and/or arbitrary distribution. In stillfurther embodiments of the invention, different functions/elements of anM-ary orthonormal and/or orthogonal signaling alphabet may bedifferently distributed.

Embodiments of the invention provide a transmitter comprising a systemfor communicating information based upon a waveform that issubstantially devoid of a cyclostationary property. The transmitter maycomprise at least one waveform alphabet including a plurality ofelements, wherein the waveform that is substantially devoid of acyclostationary property may include at least one element of theplurality of elements of the at least one waveform alphabet. The atleast one waveform alphabet may be generated based upon at least onestatistical distribution responsive to a key and/or Time-of-Day (TOD)value.

In some embodiments, communicating information comprises associating ameasure of information with at least one element of the at least onewaveform alphabet wherein the measure of information may be a messageand/or a symbol comprising at least one bit.

In some embodiments, at least first and second elements of the pluralityof elements are substantially orthogonal therebetween and/orsubstantially orthonormal therebetween. The at least one statisticaldistribution may comprise a Normal/Gaussian, Bernoulli, Geometric,Pascal/Negative Binomial, Exponential, Erlang, Weibull, Chi-Squared, F,Student's t, Rise, Pareto, Poisson, Binomial, Uniform, Gamma, Beta,Laplace, Cauchy, Rayleigh, Maxwell and/or any other distribution.According to some embodiments, the at least one statistical distributionis truncated.

In further embodiments, the key comprises a bit sequence and in someembodiments, the bit sequence comprises a TRANsmissions SECurity(TRANSEC) and/or a COMMunications SECurity (COMMSEC) bit sequence. TheTime-of-Day (TOD) value may be based upon GPS. Generating the at leastone waveform alphabet may comprise using a predetermined algorithmand/or look-up table.

In some embodiments, an element of the plurality of elements is basedupon a plurality of time-domain and/or frequency-domain values, whereina time-domain and/or frequency-domain value of the plurality oftime-domain and/or frequency-domain values may be real, imaginary and/orcomplex.

The transmitter may further comprise a direct waveform synthesis devoidof a frequency translation, wherein the direct waveform synthesis isused to generate the at least one waveform alphabet. In someembodiments, the direct waveform synthesis comprises at least onepseudo-random generator, filter, Analog-to-Digital (A/D) converter,Digital-to-Analog (D/A) converter, Fourier transform, inverse Fouriertransform and/or orthogonalizer, wherein the Fourier transform may be aDiscrete Fourier Transform (DFT) and/or a Fast Fourier Transform (FFT)and the inverse Fourier transform may be an Inverse Discrete FourierTransform (IDFT) and/or an Inverse Fast Fourier Transform (IFFT).

In further embodiments, the orthogonalizer may be a Gram-Schmidtorthogonalizer. In still further embodiments, the at least one waveformalphabet may comprise at least two waveform alphabets. The at least onewaveform alphabet may be used over a first time interval and not usedover a second time interval, wherein the first time interval may beassociated with a Time-of-Day (TOD) value, message, symbol and/or bit.The at least one second waveform alphabet may be used over the secondtime interval and the at least one waveform alphabet and the at leastone second waveform alphabet may be different therebetween, whereindifferent comprises a difference in a time-domain and/orfrequency-domain characteristic.

In some embodiments, the transmitter may further be configured totransmit at least one second waveform during a time interval that is notassociated with communicating information, wherein the at least onesecond waveform may be devoid of a cyclostationary property and maycomprise a frequency content that is substantially the same as afrequency content of the waveform. The frequency content may be a powerspectral density.

In some embodiments, the transmitter is fixed, mobile, portable,transportable, installed in a vehicle and/or installed in a space-basedcomponent such as a satellite. The vehicle may be a land-mobile vehicle,a maritime vehicle, an aeronautical vehicle and/or an unmanned vehicle.

In further embodiments, the transmitter being devoid of acyclostationary property comprises being devoid of a chipping rate. Thetransmitter may further include Forward Error Correction (FEC) encoding,bit repetition, bit interleaving, bit-to-symbol conversion, symbolrepetition, symbol interleaving, symbol-to-waveform mapping, waveformrepetition and/or waveform interleaving and, according to someembodiments, the transmitter may include communicating informationwirelessly and/or communicating spread-spectrum information.

In some embodiments, the waveform comprises a first plurality offrequencies over a first time interval and a second plurality offrequencies over a second time interval, wherein the first plurality offrequencies differ from the second plurality of frequencies in at leastone frequency. In further embodiments, at least some frequencies of thefirst and/or second plurality of frequencies are also used by a secondtransmitter, wherein the second transmitter may be a transmitterassociated with a commercial and/or military communications system.

The at least one waveform alphabet may be used deterministically and/orpseudo-randomly, wherein used deterministically and/or pseudo-randomlymay comprise usage of the at least one waveform alphabet responsive to aTime-of-Day (TOD) value, a pseudo-random selection and/or a usage of oneor more waveform alphabets other than the at least one waveformalphabet. In some embodiments, usage comprises usage of at least oneelement of the plurality of elements of the at least one waveformalphabet.

In some embodiments, the transmitter comprises a synthesis associatedwith the waveform that is substantially devoid of a frequencytranslation. The synthesis may include a plurality of operations thatare used to form the waveform, the plurality of operations not includinga frequency translation and the transmitter communicating informationbased upon the waveform without subjecting the waveform to a frequencytranslation.

According to some embodiments of the invention, the plurality ofoperations include generating values pseudo-randomly, a Fouriertransform, a Discrete Fourier Transform (DFT), a Fast Fourier Transform(FFT), an inverse Fourier transform, an Inverse Discrete FourierTransform (IDFT), an Inverse Fast Fourier Transform (IFFT), ForwardError Correction (FEC) encoding, bit interleaving, bit-to-symbolconversion, symbol interleaving, symbol-to-waveform mapping, waveformrepetition, filtering, amplification and/or waveform interleaving. Insome embodiments, generating values pseudo-randomly comprises generatingat least one value responsive to a Time-of-Day (TOD) value and/or a keyinput.

In further embodiments, generating at least one value pseudo-randomlycomprises generating at least one value based upon at least onestatistical distribution, wherein the at least one statisticaldistribution may comprise a Normal/Gaussian, Bernoulli, Geometric,Pascal/Negative Binomial, Exponential, Erlang, Weibull, Chi-Squared, F,Student's t, Rise, Pareto, Poisson, Binomial, Uniform, Gamma, Beta,Laplace, Cauchy, Rayleigh, Maxwell and/or any other distribution and theat least one statistical distribution may be truncated. The at least onevalue may be a time-domain and/or frequency-domain value and the atleast one value may be real, imaginary and/or complex. The at least onevalue may be based upon at least one statistical distribution.

Embodiments of the invention provide a transmitter comprising asynthesis block and a transmission block, wherein the synthesis block isconfigured to synthesize at least one alphabet based upon at least onestatistical distribution and the transmission block is configured totransmit a waveform based upon the at least one alphabet. In someembodiments the waveform may be devoid of a cyclostationary property andthe at least one alphabet may comprise a plurality of elements and eachelement of the plurality of elements may be devoid of a cyclostationaryproperty. The synthesis block may be a direct synthesis block that doesnot include a frequency translation function and the transmission blockmay not include a frequency translation function.

In some embodiments, the at least one statistical distribution comprisesa Normal/Gaussian, Bernoulli, Geometric, Pascal/Negative Binomial,Exponential, Erlang, Weibull, Chi-Squared, F, Student's t, Rise, Pareto,Poisson, Binomial, Uniform, Gamma, Beta, Laplace, Cauchy, Rayleigh,Maxwell and/or any other distribution and the at least one statisticaldistribution may be truncated.

In further embodiments, the at least one alphabet comprises a pluralityof elements and at least a first and second element of the plurality ofelements are substantially orthogonal therebetween. In still furtherembodiments, substantially orthogonal comprises substantiallyorthonormal. The at least one alphabet may be generated based upon theat least one statistical distribution responsive to a key and/orTime-of-Day (TOD) value and may be used by the transmitter forcommunicating information. In some embodiments, communicatinginformation comprises associating a measure of information with at leastone element of the at least one alphabet, wherein the measure ofinformation may be a message and/or symbol comprising at least one bit.The key may comprise a bit sequence and the bit sequence may comprise aTRANsmissions SECurity (TRANSEC) and/or a COMMunications SECurity(COMMSEC) bit sequence. The Time-of-Day (TOD) value may be based uponGPS.

In some embodiments, generating the at least one alphabet comprisesusing a predetermined algorithm and/or a look-up table. In furtherembodiments, an element of the plurality of elements is based upon aplurality of time-domain and/or frequency-domain values, wherein atime-domain and/or frequency-domain value of the plurality oftime-domain and/or frequency-domain values may be real, imaginary and/orcomplex.

In still other embodiments, the synthesis block comprises a directwaveform synthesis devoid of a frequency translation, wherein the directwaveform synthesis is used to generate the at least one alphabet. Thedirect waveform synthesis may comprise at least one pseudo-randomgenerator, filter, Analog-to-Digital (A/D) converter, Digital-to-Analog(D/A) converter, Fourier transform, inverse Fourier transform and/ororthogonalizer. The Fourier transform may be a Discrete FourierTransform (DFT) and/or a Fast Fourier Transform (FFT) and the inverseFourier transform may be an Inverse Discrete Fourier Transform (IDFT)and/or an Inverse Fast Fourier Transform (IFFT). The orthogonalizer maybe a Gram-Schmidt orthogonalizer.

In further embodiments, the at least one alphabet comprises at least twoalphabets. The at least one alphabet may be used over a first timeinterval and not used over a second time interval, wherein the firsttime interval may be associated with a Time-of-Day (TOD) value, message,symbol and/or bit. At least one second alphabet may be used over thesecond time interval. The at least one alphabet and the at least onesecond alphabet may be different therebetween, wherein different maycomprise a difference in a time-domain and/or frequency-domaincharacteristic.

In still further embodiments, at least one second waveform istransmitted during a time interval that is not associated withcommunicating information, wherein the at least one second waveform maybe devoid of a cyclostationary property and may comprise a frequencycontent that is substantially the same as a frequency content of thewaveform. The frequency content may be a power spectral density.

According to some embodiments, the transmitter is fixed, mobile,portable, transportable, installed in a vehicle and/or installed in asatellite. The vehicle may be a land-mobile vehicle, a maritime vehicle,an aeronautical vehicle and/or an unmanned vehicle. In furtherembodiments, devoid of a cyclostationary property comprises devoid of achipping rate.

In accordance with some embodiments, the transmitter further comprisesForward Error Correction (FEC) encoding, bit repetition, bitinterleaving, bit-to-symbol conversion, symbol repetition, symbolinterleaving, symbol-to-waveform mapping, waveform repetition and/orwaveform interleaving. In accordance with other embodiments,communicating information comprises communicating informationwirelessly. In further embodiments, communicating information comprisescommunicating spread-spectrum information. According to furtherembodiments, the waveform comprises a first plurality of frequenciesover a first time interval and a second plurality of frequencies over asecond time interval, wherein the first plurality of frequencies differfrom the second plurality of frequencies in at least one frequency.

In some embodiments, at least some frequencies of the first and/orsecond plurality of frequencies are also used by a second transmitter.The second transmitter may be a transmitter of a commercial and/or amilitary communications system. In other embodiments, the at least onealphabet is used deterministically and/or pseudo-randomly, wherein useddeterministically and/or pseudo-randomly may comprise usage of the atleast one alphabet responsive to a Time-of-Day (TOD) value, apseudo-random selection and/or a usage of one or more alphabets otherthan the at least one alphabet. In further embodiments, usage comprisesusage of at least one element of the plurality of elements of the atleast one alphabet.

In still further embodiments of the invention, a synthesis associatedwith the waveform is substantially devoid of a frequency translation.The synthesis may include a plurality of operations that may be used toform the waveform, the plurality of operations may not include afrequency translation and the transmitter may transmit the waveformwithout subjecting the waveform to a frequency translation. Theplurality of operations may include generating values pseudo-randomly, aFourier transform, a Discrete Fourier Transform (DFT), a Fast FourierTransform (FFT), an inverse Fourier transform, an Inverse DiscreteFourier Transform (IDFT), an Inverse Fast Fourier Transform (IFFT),Forward Error Correction (FEC) encoding, bit interleaving, bit-to-symbolconversion, symbol interleaving, symbol-to-waveform mapping, waveformrepetition, filtering, amplification and/or waveform interleaving.

In accordance with some embodiments, generating values pseudo-randomlycomprises generating at least one value responsive to a Time-of-Day(TOD) value and/or a key input. In further embodiments, generating atleast one value pseudo-randomly comprises generating at least one valuebased upon at least one statistical distribution, the at least onestatistical distribution comprising a Normal/Gaussian, Bernoulli,Geometric, Pascal/Negative Binomial, Exponential, Erlang, Weibull,Chi-Squared, F, Student's t, Rise, Pareto, Poisson, Binomial, Uniform,Gamma, Beta, Laplace, Cauchy, Rayleigh, Maxwell and/or any otherdistribution. In some embodiments, the at least one statisticaldistribution may be truncated. In further embodiments, the at least onevalue is a time-domain and/or frequency-domain value.

In still further embodiments of the invention, the at least one value isreal, imaginary and/or complex. The at least one value may be based uponat least one statistical distribution, wherein the at least onestatistical distribution comprises a Normal/Gaussian, Bernoulli,Geometric, Pascal/Negative Binomial, Exponential, Erlang, Weibull,Chi-Squared, F, Student's t, Rise, Pareto, Poisson, Binomial, Uniform,Gamma, Beta, Laplace, Cauchy, Rayleigh, Maxwell and/or any otherdistribution. The at least one statistical distribution may be atruncated distribution.

Embodiments of the invention provide a transmitter comprising a systemfor communicating information based upon a spread-spectrum waveform thatis substantially devoid of a chipping rate.

Other embodiments of the invention provide a receiver comprising asystem for receiving information from a transmitter, wherein theinformation is based upon a spread-spectrum waveform that issubstantially devoid of a chipping rate.

Further embodiments of the invention provide a transmitter, comprising asystem for communicating information based upon a waveform that issubstantially Gaussian distributed.

Still further embodiments of the invention provide a receiver comprisinga system for receiving information from a transmitter, wherein theinformation is based upon a waveform that is substantially Gaussiandistributed.

Additional embodiments provide a transmitter comprising a system forcommunicating information based upon a waveform that does not include acyclostationary signature.

Some embodiments provide a receiver comprising a system for receivinginformation from a transmitter, wherein the information is based upon awaveform that does not include a cyclostationary signature.

Other embodiments provide a transmitter comprising a system for mappingan information sequence onto a waveform sequence that is substantiallydevoid of a cyclostationary signature.

Further embodiments provide a receiver comprising a system for mapping awaveform sequence that is substantially devoid of a cyclostationarysignature onto an information sequence.

Still further embodiments provide a receiver comprising a system forproviding information based upon processing a waveform that issubstantially devoid of a cyclostationary property.

Additional embodiments provide a receiver comprising a system forreceiving information comprising at least one alphabet based upon atleast one statistical distribution.

Embodiments of the invention further provide a transmitter comprising asystem for transmitting a waveform, wherein the waveform is based uponat least one alphabet that is based upon at least one statisticaldistribution. The at least one statistical distribution comprises aNormal/Gaussian, Bernoulli, Geometric, Pascal/Negative Binomial,Exponential, Erlang, Weibull, Chi-Squared, F, Student's t, Rise, Pareto,Poisson, Binomial, Uniform, Gamma, Beta, Laplace, Cauchy, Rayleigh,Maxwell and/or any other distribution, wherein the at least onestatistical distribution may be truncated.

In some embodiments, the at least one alphabet comprises a plurality ofelements and at least a first and second element of the plurality ofelements are substantially orthogonal therebetween. In some embodiments,substantially orthogonal comprises substantially orthonormal.

Embodiments of the invention provide a receiver comprising a system forreceiving a waveform, wherein the waveform is based upon at least onealphabet that is based upon at least one statistical distribution. Theat least one statistical distribution comprises a Normal/Gaussian,Bernoulli, Geometric, Pascal/Negative Binomial, Exponential, Erlang,Weibull, Chi-Squared, F, Student's t, Rise, Pareto, Poisson, Binomial,Uniform, Gamma, Beta, Laplace, Cauchy, Rayleigh, Maxwell and/or anyother distribution, wherein the at least one statistical distributionmay be truncated. The at least one alphabet may comprise a plurality ofelements and at least a first and second element of the plurality ofelements may be substantially orthogonal therebetween. In someembodiments, substantially orthogonal comprises substantiallyorthonormal.

In accordance with some embodiments of the present invention, a methodof communicating information is provided, the method comprisingtransmitting and/or receiving a waveform that is substantially devoid ofa cyclostationary property. The method optionally further comprisesusing at least one waveform alphabet including a plurality of elements,wherein the waveform that is substantially devoid of a cyclostationaryproperty includes at least one element of the plurality of elements ofthe at least one waveform alphabet. In accordance with the method, theat least one waveform alphabet is optionally generated based upon atleast one statistical distribution responsive to a key and/orTime-of-Day (TOD) value. Further in accordance with the method,communicating information optionally comprises associating a measure ofinformation with at least one element of the at least one waveformalphabet. The measure of information may be a message and/or symbolcomprising at least one bit.

In accordance with the method, at least first and second elements of theplurality of elements may be substantially orthogonal therebetween,wherein substantially orthogonal may comprise substantially orthonormal.

Further in accordance with the method, the at least one statisticaldistribution optionally comprises a Normal/Gaussian, Bernoulli,Geometric, Pascal/Negative Binomial, Exponential, Erlang, Weibull,Chi-Squared, F, Student's t, Rise, Pareto, Poisson, Binomial, Uniform,Gamma, Beta, Laplace, Cauchy, Rayleigh, Maxwell and/or any otherdistribution, wherein the at least one statistical distribution may betruncated.

In some embodiments according to the method, the key comprises a bitsequence, wherein the bit sequence may comprise a TRANsmissions SECurity(TRANSEC) and/or a COMMunications SECurity (COMMSEC) bit sequence.

In further embodiments, the Time-of-Day (TOD) value is based upon GPS.In still further embodiments, generating the at least one waveformalphabet comprises using a predetermined algorithm and/or look-up table.In some embodiments, an element of the plurality of elements is basedupon a plurality of time-domain and/or frequency-domain values, whereina time-domain and/or frequency-domain value of the plurality oftime-domain and/or frequency-domain values may be real, imaginary and/orcomplex.

According to some embodiments according to the method, the methodfurther comprises a direct waveform synthesis devoid of a frequencytranslation, wherein the direct waveform synthesis is used to generatethe at least one waveform alphabet, wherein the direct waveformsynthesis may comprise at least one pseudo-random generator, filter,Analog-to-Digital (A/D) converter, Digital-to-Analog (D/A) converter,Fourier transform, inverse Fourier transform and/or orthogonalizer. Insome embodiments, the Fourier transform is a Discrete Fourier Transform(DFT) and/or a Fast Fourier Transform (FFT) and the inverse Fouriertransform is an Inverse Discrete Fourier Transform (IDFT) and/or anInverse Fast Fourier Transform (IFFT). In further embodiments, theorthogonalizer is a Gram-Schmidt orthogonalizer.

In accordance with other embodiments of the invention, the at least onewaveform alphabet comprises at least two waveform alphabets. Inaccordance with some embodiments, the at least one waveform alphabet isused over a first time interval and not used over a second timeinterval, wherein the first time interval may be associated with aTime-of-Day (TOD) value, message, symbol and/or bit.

In accordance with further embodiments of the invention, at least onesecond waveform alphabet is used over the second time interval, whereinthe at least one waveform alphabet and the at least one second waveformalphabet may be different therebetween. In some embodiments, differentcomprises a difference in a time-domain and/or frequency-domaincharacteristic.

In still other embodiments of the invention, the method comprisestransmitting at least one second waveform during a time interval that isnot associated with communicating information, wherein the at least onesecond waveform may be devoid of a cyclostationary property and maycomprise a frequency content that is substantially the same as afrequency content of the waveform. The frequency content may be a powerspectral density. In further embodiments of the invention, the methodcomprises using a transmitter that is fixed, mobile, portable,transportable, installed in a vehicle and/or installed in a satellite.The vehicle may be a land-mobile vehicle, a maritime vehicle, anaeronautical vehicle and/or an unmanned vehicle.

In some embodiments in accordance with the method, devoid of acyclostationary property comprises devoid of a chipping rate. The methodoptionally further comprises using Forward Error Correction (FEC)encoding, bit repetition, bit interleaving, bit-to-symbol conversion,symbol repetition, symbol interleaving, symbol-to-waveform mapping,waveform repetition and/or waveform interleaving. In some embodimentsaccording to the method, communicating information comprisescommunicating information wirelessly. In other embodiments according tothe method, communicating information comprises communicatingspread-spectrum information.

In further embodiments in accordance with the method, the waveformcomprises a first plurality of frequencies over a first time intervaland a second plurality of frequencies over a second time interval,wherein the first plurality of frequencies differ from the secondplurality of frequencies in at least one frequency. In some embodimentsin accordance with the method, at least some frequencies of the firstand/or second plurality of frequencies are also used by a secondtransmitter, wherein the second transmitter may be a transmitter of acommercial communications system.

In accordance with the method, the at least one waveform alphabet isoptionally used deterministically and/or pseudo-randomly, wherein useddeterministically and/or pseudo-randomly optionally comprises usage ofthe at least one waveform alphabet responsive to a Time-of-Day (TOD)value, a pseudo-random selection and/or a usage of one or more waveformalphabets other than the at least one waveform alphabet. In accordancewith the method, usage optionally comprises usage of at least oneelement of the plurality of elements of the at least one waveformalphabet.

The method optionally further comprises a synthesis associated with thewaveform that may be substantially devoid of a frequency translation. Inaccordance with the method, the synthesis optionally includes aplurality of operations that are used to form the waveform, theplurality of operations not including a frequency translation andwherein the transmitter communicates information based upon the waveformwithout subjecting the waveform to a frequency translation. Theplurality of operations may include generating values pseudo-randomly, aFourier transform, a Discrete Fourier Transform (DFT), a Fast FourierTransform (FFT), an inverse Fourier transform, an Inverse DiscreteFourier Transform (IDFT), an Inverse Fast Fourier Transform (IFFT),Forward Error Correction (FEC) encoding, bit interleaving, bit-to-symbolconversion, symbol interleaving, symbol-to-waveform mapping, waveformrepetition, filtering, amplification and/or waveform interleaving.

Generating values pseudo-randomly may comprise generating at least onevalue responsive to a Time-of-Day (TOD) value and/or a key input.Generating at least one value may comprise generating at least one valuebased upon at least one statistical distribution. The at least onestatistical distribution may comprise a Normal/Gaussian, Bernoulli,Geometric, Pascal/Negative Binomial, Exponential, Erlang, Weibull,Chi-Squared, F, Student's t, Rise, Pareto, Poisson, Binomial, Uniform,Gamma, Beta, Laplace, Cauchy, Rayleigh, Maxwell and/or any otherdistribution. In accordance with the method, the at least onestatistical distribution may be truncated.

Further in accordance with the method, the at least one value may be atime-domain and/or frequency-domain value. The at least one value may bereal, imaginary and/or complex and the at least one value may be basedupon at least one statistical distribution.

According to embodiments of the present invention, a method oftransmitting a signal is provided, the method comprising synthesizing atleast one alphabet based upon at least one statistical distribution andtransmitting a waveform based upon the at least one alphabet, whereinthe waveform may be devoid of a cyclostationary property and the atleast one alphabet may comprise a plurality of elements, each element ofthe plurality of elements may be devoid of a cyclostationary property.The synthesizing may be a direct synthesis that does not include afrequency translation function. Further according to the method, thetransmitting may not include a frequency translation function.

The at least one statistical distribution may comprise aNormal/Gaussian, Bernoulli, Geometric, Pascal/Negative Binomial,Exponential, Erlang, Weibull, Chi-Squared, F, Student's t, Rise, Pareto,Poisson, Binomial, Uniform, Gamma, Beta, Laplace, Cauchy, Rayleigh,Maxwell and/or any other distribution, wherein the at least onestatistical distribution may be truncated.

In accordance with the method, the at least one alphabet may comprise aplurality of elements and at least a first and second element of theplurality of elements may be substantially orthogonal therebetween.Substantially orthogonal may comprise substantially orthonormal.According to further embodiments of the present invention, the at leastone alphabet may be generated based upon the at least one statisticaldistribution responsive to a key and/or Time-of-Day (TOD) value and maybe used by a transmitter for communicating information. Communicatinginformation may comprise associating a measure of information with atleast one element of the at least one alphabet. The measure ofinformation may be a message and/or symbol comprising at least one bit.The key may comprise a bit sequence and the bit sequence may comprise aTRANsmissions SECurity (TRANSEC) and/or a COMMunications SECurity(COMMSEC) bit sequence.

According to still more embodiments of the present invention, theTime-of-Day (TOD) value may be based upon GPS. Generating the at leastone alphabet may comprise using a predetermined algorithm and/or look-uptable.

According to yet more embodiments of the present invention, an elementof the plurality of elements may be based upon a plurality oftime-domain and/or frequency-domain values, wherein a time-domain and/orfrequency-domain value of the plurality of time-domain and/orfrequency-domain values may be real, imaginary and/or complex.

According to further embodiments of the present invention, thesynthesizing may comprise synthesizing a direct waveform devoid of afrequency translation, wherein the direct waveform synthesizing may beused to generate the at least one alphabet. The direct waveformsynthesis may comprise at least one pseudo-random generator, filter,Analog-to-Digital (A/D) converter, Digital-to-Analog (D/A) converter,Fourier transform, inverse Fourier transform and/or orthogonalizer. TheFourier transform may be a Discrete Fourier Transform (DFT) and/or aFast Fourier Transform (FFT) and the inverse Fourier transform may be anInverse Discrete Fourier Transform (IDFT) and/or an Inverse Fast FourierTransform (IFFT). The orthogonalizer may be a Gram-Schmidtorthogonalizer.

According to still further embodiments of the present invention, the atleast one alphabet may comprise at least two alphabets. The at least onealphabet may be used over a first time interval and not used over asecond time interval. The first time interval may be associated with aTime-of-Day (TOD) value, message, symbol and/or bit. According to themethod, at least one second alphabet may be used over the second timeinterval. Further according to the method, the at least one alphabet andthe at least one second alphabet may be different therebetween, whereindifferent may comprise a difference in a time-domain and/orfrequency-domain characteristic.

According to embodiments of the present invention, the method furthercomprises transmitting at least one second waveform during a timeinterval that is not associated with communicating information, whereinthe at least one second waveform may be devoid of a cyclostationaryproperty and may comprise a frequency content that is substantially thesame as a frequency content of the waveform. The frequency content maybe a power spectral density.

According to the method, transmitting may be performed by a transmitterthat is fixed, mobile, portable, transportable, installed in a vehicleand/or installed in a satellite. The vehicle may be a land-mobilevehicle, a maritime vehicle, an aeronautical vehicle and/or an unmannedvehicle. Further according to the method, devoid of a cyclostationaryproperty may comprise devoid of a chipping rate. The method may furthercomprise use of Forward Error Correction (FEC) encoding, bit repetition,bit interleaving, bit-to-symbol conversion, symbol repetition, symbolinterleaving, symbol-to-waveform mapping, waveform repetition and/orwaveform interleaving and communicating information according to themethod may comprise communicating information wirelessly. In someembodiments, communicating information comprises communicatingspread-spectrum information.

Still further according to the method, the waveform may comprise a firstplurality of frequencies over a first time interval and a secondplurality of frequencies over a second time interval, wherein the firstplurality of frequencies differ from the second plurality of frequenciesin at least one frequency. At least some frequencies of the first and/orsecond plurality of frequencies may also used by a second transmitter.The second transmitter may be a transmitter of a commercialcommunications system.

According to embodiments of the present invention, the at least onealphabet may be used deterministically and/or pseudo-randomly, whereinused deterministically and/or pseudo-randomly may comprise usage of theat least one alphabet responsive to a Time-of-Day (TOD) value, apseudo-random selection and/or a usage of one or more alphabets otherthan the at least one alphabet. According to some embodiments of thepresent invention, usage comprises usage of at least one element of theplurality of elements of the at least one alphabet. According to otherembodiments of the present invention, a synthesis associated with thewaveform is substantially devoid of a frequency translation.

In some embodiments, the synthesis includes a plurality of operationsthat are used to form the waveform, the plurality of operations notincluding a frequency translation and wherein the transmitter transmitsthe waveform without subjecting the waveform to a frequency translation.In some embodiments, the plurality of operations may include generatingvalues pseudo-randomly, a Fourier transform, a Discrete FourierTransform (DFT), a Fast Fourier Transform (FFT), an inverse Fouriertransform, an Inverse Discrete Fourier Transform (IDFT), an Inverse FastFourier Transform (IFFT), Forward Error Correction (FEC) encoding, bitinterleaving, bit-to-symbol conversion, symbol interleaving,symbol-to-waveform mapping, waveform repetition, filtering,amplification and/or waveform interleaving. Generating valuespseudo-randomly may comprise generating at least one value responsive toa Time-of-Day (TOD) value and/or a key input.

In further embodiments according to the method, generating at least onevalue pseudo-randomly comprises generating at least one value based uponat least one statistical distribution. The at least one statisticaldistribution may comprise a Normal/Gaussian, Bernoulli, Geometric,Pascal/Negative Binomial, Exponential, Erlang, Weibull, Chi-Squared, F,Student's t, Rise, Pareto, Poisson, Binomial, Uniform, Gamma, Beta,Laplace, Cauchy, Rayleigh, Maxwell and/or any other distribution. The atleast one statistical distribution may be truncated. The at least onevalue may be a time-domain and/or frequency-domain value. The at leastone value may be real, imaginary and/or complex and, according to someembodiments of the invention, the at least one value is based upon atleast one statistical distribution.

According to the method, the at least one statistical distribution maycomprise a Normal/Gaussian, Bernoulli, Geometric, Pascal/NegativeBinomial, Exponential, Erlang, Weibull, Chi-Squared, F, Student's t,Rise, Pareto, Poisson, Binomial, Uniform, Gamma, Beta, Laplace, Cauchy,Rayleigh, Maxwell and/or any other distribution. The at least onestatistical distribution may be truncated.

According to embodiments of the invention, a method of communicatinginformation may comprise transmitting and/or receiving a spread-spectrumwaveform that is substantially devoid of a chipping rate.

According to some other embodiments of the invention, a method ofreceiving information may comprise receiving a measure of aspread-spectrum waveform that is substantially devoid of a chippingrate.

According to some more embodiments of the invention, a method ofcommunicating information is provided, the method comprisingtransmitting and/or receiving a waveform that is substantially Gaussiandistributed.

According to some additional embodiments of the present invention, amethod of receiving information is provided, the method comprisingreceiving a measure of a waveform that is substantially Gaussiandistributed.

According to still more embodiments of the present invention, a methodof communicating information is provided, the method comprisingtransmitting a waveform that does not include a cyclostationarysignature.

According to yet more embodiments of the present invention, a method ofreceiving information from a transmitter is provided, the methodcomprising receiving a measure of a waveform that does not include acyclostationary signature, wherein the waveform that does not include acyclostationary signature has been transmitted by the transmitter.

According to further embodiments of the present invention, a method oftransmitting information is provided, the method comprising mapping aninformation sequence onto a waveform sequence, wherein the waveformsequence is substantially devoid of a cyclostationary signature.

According to still further embodiments, a method of receivinginformation is provided, the method comprising mapping a waveformsequence that is substantially devoid of a cyclostationary signatureonto an information sequence.

According to some embodiments of the present invention, a method ofproviding information is provided, the method comprising processing awaveform that is substantially devoid of a cyclostationary property.

According to some more embodiments of the present invention, a method ofreceiving information from a transmitter is provided, the methodcomprising receiving a measure of a signal that is based upon at leastone statistical distribution, wherein the transmitter synthesizes atleast one alphabet based upon the at least one statistical distributionand transmits the signal based upon the at least one alphabet.

According to some other embodiments of the present invention, a methodof transmitting a signal is provided, the method comprising wirelesslytransmitting a signal that is based upon at least one alphabet, whereinthe at least one alphabet is based upon at least one statisticaldistribution. The at least one statistical distribution may comprise aNormal/Gaussian, Bernoulli, Geometric, Pascal/Negative Binomial,Exponential, Erlang, Weibull, Chi-Squared, F, Student's t, Rise, Pareto,Poisson, Binomial, Uniform, Gamma, Beta, Laplace, Cauchy, Rayleigh,Maxwell and/or any other distribution. The at least one statisticaldistribution may be truncated. The at least one alphabet may comprise aplurality of elements and at least a first and second element of theplurality of elements may be substantially orthogonal therebetween,wherein substantially orthogonal may comprise substantially orthonormal.

According to embodiments of the invention, a method of processing awaveform may comprise transmitting and/or receiving the waveform,wherein the waveform is based upon at least one alphabet, the at leastone alphabet is based upon at least one statistical distribution and thewaveform and/or the at least one alphabet is/are substantially devoid ofa cyclostationary signature and/or chipping rate. The at least onestatistical distribution may comprise a Normal/Gaussian, Bernoulli,Geometric, Pascal/Negative Binomial, Exponential, Erlang, Weibull,Chi-Squared, F, Student's t, Rise, Pareto, Poisson, Binomial, Uniform,Gamma, Beta, Laplace, Cauchy, Rayleigh, Maxwell and/or any otherdistribution. In some embodiments, the at least one statisticaldistribution may be truncated.

According to some other embodiments of the present invention, the atleast one alphabet may comprise a plurality of elements and at least afirst and second element of the plurality of elements may besubstantially orthogonal therebetween, wherein substantially orthogonalmay comprise substantially orthonormal. The processing may include aplurality of operations and may be substantially devoid of a frequencytranslation. According to still more embodiments of the presentinvention, the plurality of operations may include generating valuespseudo-randomly, a Fourier transform, a Discrete Fourier Transform(DFT), a Fast Fourier Transform (FFT), an inverse Fourier transform, anInverse Discrete Fourier Transform (IDFT), an Inverse Fast FourierTransform (IFFT), Forward Error Correction (FEC) encoding, bitinterleaving, bit-to-symbol conversion, symbol interleaving,symbol-to-waveform mapping, waveform repetition, filtering,amplification and/or waveform interleaving.

According to yet more embodiments of the present invention, generatingvalues pseudo-randomly may comprise generating at least one valueresponsive to a Time-of-Day (TOD) value and/or a key input, whereingenerating at least one value may comprise generating at least one valuebased upon at least one statistical distribution. In some embodiments,the at least one statistical distribution comprises a Normal/Gaussian,Bernoulli, Geometric, Pascal/Negative Binomial, Exponential, Erlang,Weibull, Chi-Squared, F, Student's t, Rise, Pareto, Poisson, Binomial,Uniform, Gamma, Beta, Laplace, Cauchy, Rayleigh, Maxwell and/or anyother distribution. According to further embodiments of the presentinvention, the at least one statistical distribution may be truncated.

According to still further embodiments of the present invention, the atleast one value may be a time-domain and/or frequency-domain value,wherein the at least one value may be real, imaginary and/or complex.The at least one value may be based upon at least one statisticaldistribution.

Transmitting and/or receiving may comprise wirelessly transmittingand/or receiving. According to some embodiments of the presentinvention, transmitting and/or receiving may comprise transmittingand/or receiving at a space-based component, at a land-mobile vehicle,at a maritime vehicle, at an aeronautical vehicle, at an un-mannedvehicle and/or at a user device, wherein the user device may be fixed,mobile, portable, transportable and/or installed in a vehicle.

Wirelessly transmitting and/or receiving may be based upon frequenciesthat are used by a plurality of transmitters, wherein first and secondtransmitters of the plurality of transmitters may respectively beassociated with first and second systems. In some embodiments, at leastone system of the first and second systems is a commercial system usingfrequencies that are authorized for use by one or more commercialsystems and/or a military system using frequencies that are reserved foruse by one or more military systems.

Embodiments according to the invention can provide methods and/ortransmitters for communicating information based upon a waveform that issubstantially devoid of a cyclostationary property. Pursuant to theseembodiments, a method/transmitter can be provided comprising at leastone waveform alphabet including a plurality of elements, wherein thewaveform that is substantially devoid of a cyclostationary propertyincludes at least one element of the plurality of elements of the atleast one waveform alphabet.

In some embodiments according to the invention, the at least onewaveform alphabet is generated based upon at least one statisticaldistribution responsive to a key and/or Time-of-Day (TOD) value.

In some embodiments according to the invention, communicatinginformation comprises associating a measure of information with at leastone element of the at least one waveform alphabet. In some embodimentsaccording to the invention, the measure of information is a messageand/or symbol comprising at least one bit.

In some embodiments according to the invention, at least first andsecond elements of the plurality of elements are substantiallyorthogonal therebetween, wherein substantially orthogonal may, in someembodiments, comprise substantially orthonormal.

In some embodiments according to the invention, the at least onestatistical distribution comprises a Normal/Gaussian, Bernoulli,Geometric, Pascal/Negative Binomial, Exponential, Erlang, Weibull,Chi-Squared, F, Student's t, Rise, Pareto, Poisson, Binomial, Uniform,Gamma, Beta, Laplace, Cauchy, Rayleigh, Maxwell and/or any otherdistribution. In further embodiments, the at least one statisticaldistribution is truncated.

In some embodiments according to the invention, a method and/ortransmitter can be provided comprising a synthesis component and atransmission component, wherein the synthesis component synthesizes atleast one alphabet based upon at least one statistical distribution andthe transmission component transmits a waveform based upon the at leastone alphabet. In some embodiments, the waveform is devoid of acyclostationary property. In other embodiments, the at least onealphabet comprises a plurality of elements, with each element of theplurality of elements being devoid of a cyclostationary property. Instill other embodiments, the synthesis component is a direct synthesiscomponent that does not include a frequency translation function and/orthe transmission component does not include a frequency translationfunction.

Embodiments of the present invention have been described above in termsof systems, methods, devices and/or computer program products thatprovide communications devoid of cyclostationary features. However,other embodiments of the present invention may selectively providecommunications devoid of cyclostationary features. For example, ifLPI/LPD/LPE and/or minimum interference communications are desired, thennon-cyclostationary waveforms may be transmitted. However, whenLPI/LPD/LPE and/or minimum interference communications need not betransmitted, cyclostationary waveforms may be used. An indicator may beprovided to allow a receiver/transmitter to determine whethercyclostationary or non-cyclostationary waveforms are being transmittedor may be transmitted. Accordingly, a given system, method, deviceand/or computer program can operate in one of two modes, depending uponwhether LPI/LPD/LPE and/or minimum interference communications aredesired, and/or based on other parameters and/or properties of thecommunications environment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of functions of a transmitteraccording to embodiments of the present invention.

FIG. 2 is a schematic illustration of further functions of a transmitteraccording to further embodiments of the present invention.

FIG. 3 is a schematic illustration of waveform generation according toadditional embodiments of the present invention.

FIG. 4 is a schematic illustration of further functions of a transmitteraccording to further embodiments of the present invention.

FIG. 5 is a schematic illustration of additional functions of atransmitter according to additional embodiments of the presentinvention.

FIG. 6 is a schematic illustration of functions of a receiver accordingto embodiments of the present invention.

FIG. 7 is a schematic illustration of further functions of a transmitteraccording to further embodiments of the present invention.

FIG. 8 is a schematic illustration of spectrum used by a transmitteraccording to embodiments of the present invention.

FIG. 9 is a schematic illustration of further functions of a receiveraccording to further embodiments of the present invention.

FIG. 10 is a schematic illustration of a communications system basedupon one or more transmitters and one or more receivers according tofurther embodiments of the present invention.

FIGS. 11 through 14 illustrate functions of a receiver according tofurther embodiments of the present invention.

FIG. 15 is a schematic illustration of further functions of atransmitter and receiver according to further embodiments of the presentinvention.

FIG. 16 is a flowchart of operations that may be performed according tosome embodiments of the present invention.

FIG. 17 is a block diagram of a XG-CSSC system transmitter architectureaccording to various embodiments of the present invention.

FIG. 18 is a block diagram of a XG-CSSC system receiver architectureaccording to various embodiments of the present invention.

FIGS. 19( a)-19(c) illustrate a power spectral density of a XG-CSSCwaveform (a) in an interference-free environment, (b) in interferenceavoidance mode illustrating a cognitive property, and (c) following asquare-law detector illustrating featureless (cyclostationary-free)nature, according to various embodiments.

FIG. 20 illustrates a power spectral density of a conventional QPSKwaveform and a cyclostationary feature thereof.

FIG. 21 illustrates a constellation of a XG-CSSC waveform according tovarious embodiments.

FIG. 22 illustrates a histogram of transmitted symbols of a XG-CSSCwaveform corresponding to the constellation of FIG. 21 according tovarious embodiments of the invention.

FIG. 23 graphically illustrates BER vs. E_(s)/N₀ for 16-ary XG-CSSC and16-QAM spread spectrum according to various embodiments of theinvention.

FIG. 24 graphically illustrates BER vs. E_(s)/N₀ for 16-ary XG-CSSC and16-QAM Spread Spectrum subject to Co-Channel (“CC”) interferenceaccording to various embodiments of the invention. The CC interferenceconsidered is of two types: Wide-Band (“WB”) spanning the entire desiredsignal spectrum, and Band-Pass (“BP”) spanning only 20% of the desiredsignal spectrum. Interference and desired signal are assumed to haveidentical power.

FIG. 25 graphically illustrates BER vs. E_(s)/N₀ for 16-ary XG-CSSC and16-QAM Spread Spectrum subject to Band-Pass (“BP”) Co-Channelinterference according to various embodiments of the invention. The BPinterference spans 20% of the desired signal spectrum. The term“Adaptive XG-CSSC” in the legend refers to the cognitive feature ofXG-CSSC in sensing and avoiding the interference. Interference anddesired signal are assumed to have identical power

DESCRIPTION OF EMBODIMENTS ACCORDING TO THE INVENTION

Specific exemplary embodiments of the invention now will be describedwith reference to the accompanying drawings. This invention may,however, be embodied in many different forms and should not be construedas limited to the embodiments set forth herein. Rather, theseembodiments are provided so that this disclosure will be thorough andcomplete, and will fully convey the scope of the invention to thoseskilled in the art. It will be understood that two or more embodimentsof the present invention as presented herein may be combined in whole orin part to form one or more additional embodiments.

It will be understood that when an element is referred to as being“connected” or “coupled” to another element, it can be directlyconnected or coupled to the other element or intervening elements may bepresent. Furthermore, “connected” or “coupled” as used herein mayinclude wirelessly connected or coupled.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless expressly stated otherwise. Itwill be further understood that the terms “includes,” “comprises,”“including” and/or “comprising,” when used in this specification,specify the presence of stated features, integers, steps, operations,elements, and/or components, but do not preclude the presence oraddition of one or more other features, integers, steps, operations,elements, components, and/or groups thereof.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this invention belongs. It will befurther understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art and thepresent disclosure, and will not be interpreted in an idealized oroverly formal sense unless expressly so defined herein.

It will be understood that although terms such as first and second areused herein to describe various elements, these elements should not belimited by these terms. These terms are only used to distinguish oneelement from another element. Thus, a first element below could betermed a second element, and similarly, a second element may be termed afirst element without departing from the teachings of the presentinvention. As used herein, the term “and/or” includes any and allcombinations of one or more of the associated listed items. The symbol“I” is also used as a shorthand notation for “and/or”.

Moreover, as used herein the term “substantially the same” means thattwo or more entities that are being compared have commonfeatures/characteristics (e.g., are based upon a common kernel) but maynot be identical. For example, substantially the same bands offrequencies, means that two or more bands of frequencies being comparedsubstantially overlap, but that there may be some areas of non-overlap,for example at a band end. As another example, substantially the sameair interfaces means that two or more air interfaces being compared aresimilar but need not be identical. Some differences may exist in one airinterface (e.g., a satellite air interface) relative to another (e.g., aterrestrial air interface) to account for one or more differentcharacteristics that may exist between the terrestrial and satellitecommunications environments. For example, a different vocoder rate maybe used for satellite communications compared to the vocoder rate thatmay be used for terrestrial communications (i.e., for terrestrialcommunications, voice may be compressed (“vocoded”) to approximately 9to 13 kbps, whereas for satellite communications a vocoder rate ofapproximately 2 to 4 kbps, for example, may be used); a differentforward error correction coding, different interleaving depth, and/ordifferent spread-spectrum codes may also be used, for example, forsatellite communications compared to the coding, interleaving depth,and/or spread spectrum codes (i.e., Walsh codes, long codes, and/orfrequency hopping codes) that may be used for terrestrialcommunications.

The term “truncated” as used herein to describe a statisticaldistribution means that a random variable associated with thestatistical distribution is precluded from taking-on values over one ormore ranges. For example, a Normal/Gaussian distribution that is nottruncated, allows an associated random variable to take-on valuesranging from negative infinity to positive infinity with a frequency(i.e., a probability) as determined by the Normal/Gaussian probabilitydensity function. In contrast, a truncated Normal/Gaussian distributionmay allow an associated random variable to take-on values ranging from,for example, V₁ to V₂ (−∞<V₁, V₂<∞) in accordance with a Normal/Gaussiandistribution, and preclude the random variable from taking-on valuesoutside the range from V₁ to V₂. Furthermore, a truncated distributionmay allow an associated random variable to take-on values over aplurality of ranges (that may be a plurality of non-contiguous ranges)and preclude the random variable from taking-on values outside of theplurality of ranges.

As used herein, the term “transmitter” and/or “receiver” include(s)transmitters/receivers of cellular and/or satellite terminals with orwithout a multi-line display; Personal Communications System (PCS)terminals that may include data processing, facsimile and/or datacommunications capabilities; Personal Digital Assistants (PDA) that caninclude a radio frequency transceiver and/or a pager, Internet/Intranetaccess, Web browser, organizer, calendar and/or a Global PositioningSystem (GPS) receiver; and/or conventional laptop and/or palmtopcomputers or other appliances, which include a radio frequencytransceiver. As used herein, the term “transmitter” and/or “receiver”also include(s) any other radiating device, equipment and/or source thatmay have time-varying and/or fixed geographic coordinates and/or may beportable, transportable, installed in a vehicle (aeronautical, maritime,or land-based) and/or situated/configured to operate locally and/or in adistributed fashion at any location(s) on earth, vehicles (land-mobile,maritime and/or aeronautical) and/or in space. A transmitter and/orreceiver also may be referred to herein as a “terminal”. As used herein,the term “space-based” component and/or “space-based” system include(s)one or more satellites and/or one or more other objects and/or platforms(such as airplanes, balloons, unmanned vehicles, space crafts, missiles,etc.) that have a trajectory above the earth at any altitude.

Some embodiments of the present invention may arise from recognitionthat it may be desirable to communicate information based upon awaveform that is substantially devoid of a cyclostationary property. Asused herein to describe a waveform, the term “cyclostationary” meansthat the waveform comprises at least one signature/pattern that may be arepeating signature/pattern. Examples of a repeating signature/patternare a bit rate, a symbol rate, a chipping rate and/or a pulse shape(e.g., a Nyquist pulse shape) that may be associated with abit/symbol/chip. For example, each of the well known terrestrialcellular air interfaces of GSM and CDMA (cdma2000 or W-CDMA) comprises abit rate, a symbol rate, a chipping rate and/or a predetermined andinvariant pulse shape that is associated with the bit/symbol/chip and,therefore, comprise a cyclostationary property/signature. In contrast, awaveform that represents a random (or pseudo-random) noise process doesnot comprise a bit rate, a symbol rate, a chipping rate and/or apredetermined and invariant pulse shape and is, therefore, substantiallydevoid of a cyclostationary property/signature. According to someembodiments of the present invention, non-cyclostationary waveforms maybe used, particularly in those situations where LPI, LPD, LPE, private,secure and/or minimum interference communications are desirable.

Conventional communications systems use waveforms that are substantiallycyclostationary. This is primarily due to a methodology of transmittinginformation wherein a unit of information (i.e., a specific bit sequencecomprising one or more bits) is mapped into (i.e., is associated with) aspecific waveform shape (i.e., a pulse) and the pulse is transmitted bya transmitter in order to convey to a receiver the unit of information.Since there is typically a need to transmit a plurality of units ofinformation in succession, a corresponding plurality of pulses aretransmitted in succession. Any two pulses of the plurality of pulses maydiffer therebetween in sign, phase and/or magnitude, but a waveformshape that is associated with any one pulse of the plurality of pulsesremains substantially invariant from pulse to pulse and a rate of pulsetransmission also remains substantially invariant (at least over a timeinterval). The methodology of transmitting (digital) information asdescribed above has its origins in, and is motivated by, the way Morsecode evolved and was used to transmit information. Furthermore, themethodology yields relatively simple transmitter/receiverimplementations and has thus been adopted widely by many communicationssystems. However, the methodology suffers from generatingcyclostationary features/signatures that are undesirable if LPE/LPI/LPDand/or minimum interference communications are desirable. Embodiments ofthe present invention arise from recognition that communications systemsmay be based on a different methodology that is substantially devoid oftransmitting a modulated carrier, a sequence of substantially invariantpulse shapes and/or a chipping rate and that even spread-spectrumcommunications systems may be configured to transmit/receivespread-spectrum information using waveforms that are devoid of achipping rate.

A publication by W. A. Gardner, entitled “Signal Interception: AUnifying Theoretical Framework for Feature Detection,” IEEE Transactionson Communications, Vol. 36, No. 8, August 1988, notes in the Abstractthereof that the unifying framework of the spectral correlation theoryof cyclostationary signals is used to present a broad treatment of weakrandom signal detection for interception purposes. The relationshipsamong a variety of previously proposed ad hoc detectors, optimumdetectors, and newly proposed detectors are established. Thespectral-correlation-plane approach to the interception problem is putforth as especially promising for detection, classification, andestimation in particularly difficult environments involving unknown andchanging noise levels and interference activity. A fundamental drawbackof the popular radiometric methods in such environments is explained.According to some embodiments of the invention, it may be desirable tobe able to communicate information using waveforms that do notsubstantially include a cyclostationary feature/signature in order tofurther reduce the probability of intercept/detection/exploitation of acommunications system/waveform that is intended for LPI/LPD/LPEcommunications.

There are at least two potential advantages associated with signaldetection, identification, interception and/or exploitation based oncyclic spectral analysis compared with the energy detection(radiometric) method: (1) A cyclic signal feature (i.e., chip rateand/or symbol rate) may be discretely distributed even if a signal hascontinuous distribution in a power spectrum. This implies that signalsthat may have overlapping and/or interfering features in a powerspectrum may have a non-overlapping and distinguishable feature in termsof a cyclic characteristic, (2) A cyclic signal feature associated witha signal's cyclostationary property, may be identified via a “cyclicperiodogram.” The cyclic periodogram of a signal is a quantity that maybe evaluated from time-domain samples of the signal, a frequency-domainmapping such as, for example, a Fast Fourier Transform (FFT), and/ordiscrete autocorrelation operations. Since very large point FFTs and/orautocorrelation operations may be implemented using Very Large ScaleIntegration (VLSI) technologies, Digital Signal Processors (DSPs) and/orother modern technologies, a receiver of an interceptor may beconfigured to perform signal Detection, Identification, Interceptionand/or Exploitation (D/I/I/E) based on cyclic feature detectionprocessing.

Given the potential limitation(s) of the radiometric approach and thepotential advantage(s) of cyclic feature detection technique(s) it isreasonable to expect that a sophisticated interceptor may be equippedwith a receiver based on cyclic feature detection processing. It is,therefore, of potential interest and potential importance to developcommunications systems capable of communicating information devoid ofcyclostationary properties/signatures to thereby render cyclic featuredetection processing by an interceptor substantially ineffective.

FIG. 1 illustrates embodiments of generating a communications alphabetcomprising M distinct pseudo-random, non-cyclostationary, orthogonaland/or orthonormal waveforms. As illustrated in FIG. 1, responsive to a“key” input (such as, for example, a TRANsmissions SECurity (TRANSEC)key input, a COMMunications SECurity (COMMSEC) key input and/or anyother key input), a Pseudo-Random Waveform Generator (PRWG) may be usedto generate a set of M distinct pseudo-random waveforms, which may,according to some embodiments of the invention, represent M ensembleelements of a Gaussian-distributed random (or pseudo-random) process.The M distinct pseudo-random waveforms (i.e., the M ensemble elements)may be denoted as {S(t)}={S₁(t), S₂(t), . . . , S_(M)(t)}; 0≦t≦τ. Theset of waveforms {S(t)} may be a band-limited set of waveforms having aone-sided bandwidth less than or equal to B Hz. As such, a number ofdistinct orthogonal and/or orthonormal waveforms that may be generatedfrom the set {S(t)} may, in accordance with established Theorems, beupper-bounded by CτB, where C≧2 (see, for example, P. M. Dollard, “Onthe time-bandwidth concentration of signal functions forming givengeometric vector configurations,” IEEE Transactions on InformationTheory, IT-10, pp. 328-338, October 1964; also see H. J. Landau and H.O. Pollak, “Prolate spheroidal wave functions, Fourier analysis anduncertainty—The dimension of the space of essentially time-andband-limited signals,” Bell System Technical Journal, 41, pp. 1295-1336,July 1962). It will be understood that in some embodiments of thepresent invention, the key input may not be used and/or may not exist.In such embodiments, one or more Time-of-Day (TOD) values may be usedinstead of the key input. In other embodiments, a key input and one ormore TOD values may be used. In still other embodiments, yet othervalues may be used.

In accordance with some embodiments of the present invention, the j^(th)element of the set of waveforms {S(t)}, j=1, 2, . . . , M; may begenerated by a respective j^(th) PRWG in response to a respective j^(th)key input and/or TOD value, as illustrated in FIG. 2. In someembodiments according to FIG. 2, each of the PRWG is the same PRWG andeach key differs relative to each other key. In other embodiments, eachkey is the same key and each PRWG differs relative to each other PRWG.In further embodiments of FIG. 2, each key differs relative to eachother key and each PRWG also differs relative to each other PRWG. Othercombinations and sub-combinations of these embodiments may be provided.In still other embodiments, a single PRWG and a single key may be usedto generate a “long” waveform S_(L)(t) which may be segmented into Moverlapping and/or non-overlapping components to form a set of waveforms{S(t)}, as illustrated in FIG. 3. Note that any τ-sec. segment ofS_(L)(t) may be used to define S₁(t). Similarly, any τ-sec. segment ofS_(L)(t) may be used to define S₂(t), with possibly the exception of thesegment used-to define S₁(t), etc. The choices may be predeterminedand/or based on a key input.

In some embodiments of the invention, a new set of waveforms {S(t)} maybe formed periodically, non-periodically, periodically over a first timeinterval and non-periodically over a second time interval and/orperiodically but with a jitter imposed on a periodicity interval,responsive one or more TOD values that may, for example, be derived fromprocessing of Global Positioning System (GPS) signals, and/or responsiveto a transmission of a measure of at least one of the elements of{S(t)}. In some embodiments, a processor may be operatively configuredas a background operation, generating new sets of waveforms {S(t)}, andstoring the new sets of waveforms {S(t)} in memory to be accessed andused as needed. In further embodiments, a used set of waveforms {S(t)}may be discarded and not used again, whereas in other embodiments, aused set of waveforms {S(t)} may be placed in memory to be used again ata later time. In some embodiments, some sets of waveforms {S(t)} areused once and then discarded, other sets of waveforms {S(t)} are notused at all, and still other sets of waveforms {S(t)} are used more thanonce. Finally, in some embodiments, the waveform duration τ and/or thewaveform bandwidth B may vary between different sets of waveforms,transmission intervals and/or elements of a given set of waveforms.

Still referring to FIG. 1, the set of substantially continuous-timewaveforms {S(t)}={S₁(t), S₂(t), . . . , S_(M)(t)}; 0≦t≦τ; may, accordingto some embodiments of the present invention, be transformed from asubstantially continuous-time representation to a substantiallydiscrete-time representation using, for example, one or moreAnalog-to-Digital (A/D) converters and/or one or more Sample-and-Hold(S/H) circuits, to generate a corresponding substantially discrete-timeset of waveforms {S(nT)}={S₁(nT), S₂(nT), . . . , S_(M)(nT)}; n=1, 2, .. . , N; nT≦τ. A Gram-Schmidt orthogonalizer and/or orthonormalizerand/or any other orthogonalizer and/or orthonormalizer, may then beused, as illustrated in FIG. 1, to generate a set of waveforms{U(nT)}={U₁(nT), U₂(nT), . . . , U_(M)(nT)}; n=1, 2, . . . , N; nT≦τthat are orthogonal and/or orthonormal therebetween. The GSO and/orother orthogonalization and/or orthonormalization procedure(s) are knownto those skilled in the art and need not be described further herein(see, for example, Simon Haykin, “Adaptive Filter Theory,” at 173, 301,497; 1986 by Prentice-Hall; and Bernard Widrow and Samuel D. Stearns“Adaptive Signal Processing,” at 183; 1985 by Prentice-Hall, Inc.).

It will be understood that the sampling interval T may be chosen inaccordance with Nyquist sampling theory to thereby preserve by thediscrete-time waveforms {S(nT)} all, or substantially all, of theinformation contained in the continuous-time waveforms {S(t)}. It willalso be understood that, in some embodiments of the invention, thesampling interval T may be allowed to vary over the waveform duration τ,between different waveforms of a given set of waveforms and/or betweendifferent sets of waveforms. Furthermore, the waveform duration τ may beallowed to vary, in some embodiments, between different waveforms of agiven set of waveforms and/or between different sets of waveforms. Insome embodiments of the present invention, {S(nT)}={S₁(nT), S₂(nT), . .. , S_(M)(nT)}; n=1, 2, . . . , N; nT≦τ may be generated directly in adiscrete-time domain by configuring one or more Pseudo-Random NumberGenerators (PRNG) to generate S_(j)(nT); n=1, 2, . . . , N; nT≦τ foreach value of j (j=1, 2, . . . , M). The one or more PRNG may beconfigured to generate S_(j)(nT); n=1, 2, . . . , N; j=1, 2, . . . , M,based upon at least one statistical distribution. In some embodimentsaccording to the present invention, the at least one statisticaldistribution comprises a Normal/Gaussian, Bernoulli, Geometric,Pascal/Negative Binomial, Exponential, Erlang, Weibull, Chi-Squared, F,Student's t, Rise, Pareto, Poisson; Binomial, Uniform, Gamma, Beta,Laplace, Cauchy, Rayleigh, Maxwell and/or any other distribution. Infurther embodiments, the at least one statistical distribution istruncated. In still further embodiments, the at least one statisticaldistribution depends upon a value of the index j and/or n (i.e., the atleast one statistical distribution is a function of (j, n)).

In still further embodiments of the present invention, {S(nT)} may begenerated by configuring one or more PRNG to generate real, imaginaryand/or complex values that are then subjected to a linear and/ornon-linear transformation to generate S_(j)(nT); n=1, 2, . . . , N; j=1,2, . . . , M. In some embodiments of the present invention, thetransformation comprises a Fourier transformation. In furtherembodiments, the transformation comprises an inverse Fouriertransformation. In still further embodiments, the transformationcomprises an Inverse Fast Fourier Transformation (IFFT). The real,imaginary and/or complex values may be based upon at least onestatistical distribution. The at least one statistical distribution maycomprise a Normal/Gaussian, Bernoulli, Geometric, Pascal/NegativeBinomial, Exponential, Erlang, Weibull, Chi-Squared, F, Student's t,Rise, Pareto, Poisson, Binomial, Uniform, Gamma, Beta, Laplace, Cauchy,Rayleigh, Maxwell and/or any other distribution and the at least onestatistical distribution may be truncated. In still further embodiments,the at least one statistical distribution depends upon a value of theindex j and/or n (i.e., the at least one statistical distribution is afunction of (j, n)).

The set {U(nT)}={U₁(nT), U₂(nT), . . . , U_(M)(nT)}; n=1, 2, N; NT≦τ,may be used, in some embodiments of the present invention, to define anM-ary pseudo-random and non-cyclostationary alphabet. As illustrated inFIG. 4, an information symbol I_(k), occurring at a discrete time k (forexample, at t=kτ or, more generally, if the discrete timeepochs/intervals are variable, at t=τ_(k)), and having one of M possibleinformation values, {I₁, I₂, . . . , I_(M)}, may be mapped onto one ofthe M waveforms of the alphabet {U₁(nT), U₂(nT), . . . , U_(M)(nT)};n=1, 2, . . . , N; NT≦τ. For example, in some embodiments, if I_(k)=I₂,then during the k^(th) signaling interval the waveform U₂(nT) may betransmitted; n=1, 2, . . . , N; NT≦τ. It will be understood thattransmitting the waveform U₂(nT) comprises transmitting substantiallyall of the elements (samples) of the waveform U₂(nT) whereinsubstantially all of the elements (samples) of the waveform U₂(nT) meanstransmitting U₂(T), U₂(2T), . . . , and U₂(NT). Furthermore, it will beunderstood that any unambiguous mapping between the M possibleinformation values of I_(k) and the M distinct waveforms of the M-aryalphabet, {U₁(nT), U₂(nT), . . . , U_(M)(nT)}, may be used tocommunicate information to a receiver (destination) provided that thereceiver also has knowledge of the mapping. It will also be appreciatedthat the ordering or indexing of the alphabet elements and theunambiguous mapping between the M possible information values of I_(k)and the M distinct waveforms of the M-ary alphabet may be arbitrary, aslong as both transmitter (source) and receiver (destination) haveknowledge of the ordering and mapping.

In some embodiments of the invention, the information symbol I_(k), maybe constrained to only two possible values (binary system). In suchembodiments of the invention, the M-ary alphabet may be a binary (M=2)alphabet comprising only two elements, such as, for example, {U₁(nT),U₂(nT)}. In other embodiments of the invention, while an informationsymbol, I_(k), is allowed to take on one of M distinct values (M≧2) thealphabet comprises more than M distinct waveforms, that may, accordingto embodiments of the invention be orthogonal/orthonormal waveforms,{U₁(nT), U₂(nT), . . . , U_(L)(nT)}; L>M, to thereby increase a distancebetween a set of M alphabet elements that are chosen and used tocommunicate information and thus allow an improvement of acommunications performance measure such as, for example, an error rate,a propagations distance and/or a transmitted power level. It will beunderstood that in some embodiments, the number of distinct values thatmay be made available to an information symbol to thereby allow theinformation symbol to communicate one or more bits of information, maybe reduced or increased responsive to a channel state such as, forexample an attenuation, a propagation distance and/or an interferencelevel. In further embodiments, a number of distinct elements comprisingan alphabet may also change responsive to a channel state. In someembodiments, as a number of information symbol states (values) decreasesa number of distinct elements comprising an alphabet increases, tothereby provide further communications benefit(s) such as, for example,a lower bit error rate, a longer propagation distance, reducedtransmitted power, etc.

It will be understood that at least some conventional transmitterfunctions comprising, for example, Forward Error Correction (FEC)encoding, interleaving, data repetition, filtering, amplification,modulation, frequency translation, scrambling, frequency hopping, etc.,although not shown in FIGS. 1 through 4, may also be used in someembodiments of the present invention to configure an overall transmitterchain. At least some of these conventional transmitter functions may beused, in some embodiments, in combination with at least some of thesignal processing functions of FIG. 1 through FIG. 4, to specify anoverall transmitter signal processing chain. For example, an informationbit sequence may be FEC encoded using, for example, a convolutionalencoder, interleaved and/or bit-to-symbol converted to define a sequenceof information symbols, {I_(k)}. The sequence of information symbols,{L}, may then be mapped onto a waveform sequence {U_(k)}, as illustratedin FIG. 4. At least some, and in some embodiments all, of the elementsof the waveform sequence {U_(k)} may then be repeated, at least once, toincrease a redundancy measure, interleaved, filtered, frequencytranslated, amplified and/or frequency-hopped, for example, (notnecessarily in that order) prior to being radiated by an antenna of thetransmitter. An exemplary embodiment of a transmitter comprisingconventional signal functions in combination with at least some of thesignal processing functions of FIG. 1 through FIG. 4 is illustrated inFIG. 5.

A receiver (destination) that is configured to receive communicationsinformation from a transmitter (source) comprising functions of FIG. 1through FIG. 4, may be equipped with sufficient information to generatea matched filter bank responsive to the M-ary alphabet {U₁(nT), U₂(nT),. . . , U_(M)(nT)} of FIG. 4. Such a receiver may be substantiallysynchronized with one or more transmitters using, for example,GPS-derived timing information. Substantial relative synchronism betweena receiver and at least one transmitter may be necessary to reliablygenerate/update at the receiver the M-ary alphabet functions {U₁(nT),U₂(nT), . . . , U_(M)(nT)} and/or the matched filter bank to therebyprovide the receiver with substantial optimum reception capability.

In some embodiments of the invention, all transmitters and receivers aresubstantially synchronized using GPS-derived timing information. It willbe understood that a receiver may be provided with the appropriate keysequence(s) and the appropriate signal processing algorithms to therebyresponsively form and/or update the M-ary alphabet functions and/or thematched filter bank. It will also be understood that a receiver may alsobe configured with an inverse of conventional transmitter functions thatmay be used by a transmitter. For example, if, in some embodiments, atransmitter is configured with scrambling, interleaving of data andfrequency hopping, then a receiver may be configured with the inverseoperations of de-scrambling, de-interleaving of data and frequencyde-hopping. An exemplary embodiment of a receiver, which may correspondto the exemplary transmitter embodiment of FIG. 5, is illustrated inFIG. 6.

FIG. 7 illustrates elements of a communications transmitter according tofurther embodiments of the invention. As shown in FIG. 7, followingconventional operations of Forward Error Correction (FEC) encoding, bitinterleaving and bit-to-symbol conversion (performed on an input bitsequence {b} to thereby form an information symbol sequence {I_(k)}),the information symbol sequence {I_(k)} is mapped onto anon-cyclostationary waveform sequence {U_(k)(nT)} using a first M-arynon-cyclostationary orthonormal alphabet (Alphabet 1). An element of{U_(k)(nT)} may then be repeated (at least once), as illustrated in FIG.7, using a second M-ary non-cyclostationary orthonormal alphabet(Alphabet 2), interleaved, transformed to a continuous-time domainrepresentation, filtered, amplified (not necessarily in that order) andtransmitted. The repeat of an element of {U_(k)(nT)} may be performedusing a different alphabet (Alphabet 2) in order to reduce or eliminatea cyclostationary feature/signature in the transmitted waveform. For atleast the same reason, the at least two alphabets of FIG. 7 may bereplaced by new alphabets following the transmission of a predeterminednumber of waveform symbols. In some embodiments, the predeterminednumber of waveform symbols is one. As stated earlier, a large reservoirof alphabets may be available and new alphabet choices may be madefollowing the transmission of the predetermined number of waveformsymbols and/or at predetermined TOD values.

According to some embodiments of the invention, the M-arynon-cyclostationary orthonormal alphabet waveforms may be broadbandwaveforms as illustrated in FIG. 8. FIG. 8 illustrates a power spectraldensity of a broadband waveform defining the M-ary non-cyclostationaryorthonormal alphabet (such as, for example, waveform S_(L)(t) of FIG.3), over frequencies of, for example, an L-band (e.g., from about 1525MHz to about 1660.5 MHz). However, FIG. 8 is for illustrative purposesonly and the power spectral density of S_(L)(t) and/or any other set ofwaveforms used to define the M-ary non-cyclostationary orthonormalalphabet may be chosen to exist over any other frequency range and/orinterval(s). In some embodiments, different alphabets may be definedover different frequency ranges/intervals (this feature may provideintrinsic frequency hopping capability). As is further illustrated inFIG. 8 (second trace), certain frequency intervals that warrantprotection (or additional protection) from interference, such as, forexample, a GPS frequency interval, may be substantially excluded fromproviding frequency content for the generation of the M-arynon-cyclostationary orthonormal alphabets. It will be appreciated thatthe transmitter embodiment of FIG. 7 illustrates a “direct synthesis”transmitter in that the transmitter directly synthesizes a waveform thatis to be transmitted, without resorting to up-conversion, frequencytranslation and/or carrier modulation functions. This aspect may furtherenhance the LPI/LPD/LPE feature(s) of a communications system.

In embodiments of the invention where a bandwidth of a signal to betransmitted by a transmitter (such as the transmitter illustrated inFIG. 7) exceeds a bandwidth limit associated with an antenna and/orother element of the transmitter, the signal may bedecomposed/segmented/divided into a plurality of components, eachcomponent of the plurality of components having a bandwidth that issmaller than the bandwidth of the signal. Accordingly, a transmitter maybe configured with a corresponding plurality of antennas and/or acorresponding plurality of other elements to transmit the plurality ofcomponents. Analogous operations for reception may be included in areceiver.

In some embodiments of the invention, a receiver (destination) that isconfigured to receive communications information from a transmitter(source) comprising the functionality of FIG. 7, may be provided withsufficient information to generate a matched filter bank correspondingto the transmitter waveform set of the M-ary alphabet {U₁(nT), U₂(nT), .. . , U_(M)(nT)}. Such a receiver may be substantially synchronized withthe transmitter using GPS-derived timing information (i.e., TOD). FIG. 9illustrates elements of such a receiver, according to exemplaryembodiments of the present invention. As illustrated in FIG. 9,following front-end filtering, amplification and Analog-to-Digital (A/D)and/or discrete-time conversion of a received waveform, a matched-filterbank, comprising matched filters reflecting the TOD-dependent waveformalphabets used by the transmitter, is used for detection of information.The receiver may have information regarding what waveform alphabet thetransmitter may have used as a function of TOD. As such, the receiver,operating in substantial TOD synchronism with the transmitter, may knowto configure the matched-filter bank with the appropriate(TOD-dependent) matched filter components to thereby achieve optimum ornear optimum signal detection. Following matched-filter detection,symbol de-interleaving and symbol repeat combination, soft decisions ofa received symbol sequence may be made, followed by bit de-interleavingand bit decoding, to thereby generate an estimate of a transmittedinformation bit sequence.

In accordance with some embodiments of the invention, a receiverarchitecture, such as, for example, the receiver architectureillustrated in FIG. 9, may further configure a matched filter bank toinclude a “rake” matched filter architecture, to thereby resolvemultipath components and increase or maximize a desired received signalenergy subject to multipath fading channels. Owing to the broadbandnature of the communications alphabets, in accordance with someembodiments of the invention, a significant number of multipathcomponents may be resolvable. Rake matched filter architectures areknown to those skilled in the art and need not be described furtherherein (see, for example, John G. Proakis, “Digital Communications,”McGraw-Hill, 1983, section 7.5 starting at 479; also see R. Price and P.E. Green Jr. “A Communication Technique for Multipath Channels,” Proc.IRE, Vol. 46, pp. 555-570, March 1958).

FIG. 10 illustrates an operational scenario relating to a communicationssystem that may be a covert communications system, in accordance withsome embodiments of the present invention, wherein air-to-ground,air-to-air, air-to-satellite and/or satellite-to-ground communicationsmay be conducted. Ground-to-ground communications (not illustrated inFIG. 10) may also be conducted. Modes of communications may be, forexample, point-to-point and/or point-to-multipoint. A network topologythat is predetermined and/or configured in an ad hoc fashion, inaccordance with principles known to those skilled in the art, may beused to establish communications in accordance with any of theembodiments of the invention and/or combinations (or sub-combinations)thereof.

FIGS. 11 through 14 illustrate elements relating to a matched filterand/or a matched filter bank in accordance with exemplary embodiments ofthe invention, as will be appreciated by those skilled in the art. FIG.15 further illustrates elements of a transmitter/receiver combination inaccordance with further embodiments of the invention. The design andoperation of blocks that are illustrated in the block diagrams hereinand not described in detail are well known to those having skill in theart.

Embodiments of the present invention have been described above in termsof systems, methods, devices and/or computer program products thatprovide communications devoid of cyclostationary features. However,other embodiments of the present invention may selectively provide thesecommunications devoid of cyclostationary features. For example, as shownin FIG. 15, if LPI/LPD/LPE and/or minimum interference communicationsare desired, then non-cyclostationary waveforms may be transmitted.However, when LPI/LPD/LPE and/or minimum interference communicationsneed not be transmitted, cyclostationary waveforms may be used. Anindicator may be provided to allow a receiver/transmitter to determinewhether cyclostationary or non-cyclostationary waveforms are beingtransmitted or need to be transmitted. Accordingly, a given system,method, device and/or computer program can operate in one of two modes,depending upon whether LPI/LPD/LPE and/or minimum interferencecommunications are desired, and/or based on other parameters and/orproperties of the communications environment.

In still further embodiments of the present invention, a transmitter maybe configured to selectively radiate a pseudo-random noise waveform thatmay be substantially devoid of information and is distributed inaccordance with at least one statistical distribution such as, forexample, Normal/Gaussian, Bernoulli, Geometric, Pascal/NegativeBinomial, Exponential, Erlang, Weibull, Chi-Squared, F, Student's t,Rise, Pareto, Poisson, Binomial, Uniform, Gamma, Beta, Laplace, Cauchy,Rayleigh, Maxwell and/or any other distribution. The at least onestatistical distribution may be truncated and the pseudo-random noisewaveform may occupy a bandwidth that is substantially the same as abandwidth occupied by a communications waveform. The transmitter may beconfigured to selectively radiate the pseudo-random noise waveformduring periods of time during which no communications information isbeing transmitted. This may be used, in some embodiments, to create asubstantially constant/invariant ambient/background noise floor, that issubstantially independent of whether or not communications informationis being transmitted, to thereby further mask an onset of communicationsinformation transmission.

It will be understood by those skilled in the art that thecommunications systems, waveforms, methods, computer program productsand/or principles described herein may also find applications inenvironments wherein covertness may not be a primary concern.Communications systems, waveforms, methods, computer program productsand/or principles described herein may, for example, be used to provideshort-range wireless communications (that may, in accordance with someembodiments, be broadband short-range wireless communications) in, forexample, a home, office, conference and/or business environment whilereducing and/or minimizing a level of interference to one or more othercommunications services and/or systems that may be using the same,substantially the same and/or near-by frequencies as the short-rangecommunications system.

Other applications of the communications systems, waveforms, methods,computer program products and/or principles described herein will alsooccur to those skilled in the art, including, for example, radarapplications and/or cellular telecommunications applications.

In a cellular telecommunications application, for example, a cellulartelecommunications system, in accordance with communications waveformprinciples described herein, may be configured, for example, as anoverlay to one or more conventional cellular/PCS systems and/or one ormore other systems, using the frequencies of one or more licensed and/orunlicensed bands (that may also be used by the one or more conventionalcellular/PCS systems and/or the one or more other systems) tocommunicate with user equipment using broadband and/or Ultra Wide-Band(UWB) waveforms. The broadband and/or UWB waveforms may benon-cyclostationary and Gaussian-distributed, for example, in accordancewith the teachings of the present invention, to thereby reduce and/orminimize a level of interference to the one or more conventionalcellular/PCS systems and/or to the one or more other systems by theoverlay cellular telecommunications system and thereby allow the overlaycellular telecommunications system to reuse the available spectrum(which is also used by the one or more conventional cellular/PCS systemsand/or the one or more other systems) to provide communications servicesto users.

According to some embodiments of the present invention, a cellulartelecommunications system that is configured to communicate with userdevices using communications waveforms in accordance with thetransmitter, receiver and/or waveform principles described herein, is anoverlay to one or more conventional cellular/PCS systems and/or to oneor more other systems and is using the frequencies of one or morelicensed and/or unlicensed bands (also being used by the one or moreconventional cellular/PCS systems and/or the one or more other systems).The cellular telecommunications system may be further configured toprovide communications preferentially using frequencies of the one ormore licensed and/or unlicensed bands that are locally not usedsubstantially and/or are locally used substantially as guardbands and/ortransition bands by the one or more conventional cellular/PCS systemsand/or the one or more other systems, to thereby further reduce a levelof interference between the cellular telecommunications system and theone or more conventional cellular/PCS systems and/or the one or moreother systems.

As used herein, the terms “locally not used substantially” and/or“locally used substantially as guardbands and/or transition bands” referto a local service area of a base station and/or group of base stationsand/or access point(s) of the cellular telecommunications system. Insuch a service area, the cellular telecommunications system may, forexample, be configured to identify frequencies that are “locally notused substantially” and/or frequencies that are “locally usedsubstantially as guardbands and/or transition bands” by the one or moreconventional cellular/PCS systems and/or the one or more other systemsand preferentially use the identified frequencies to communicatebidirectionally and/or unidirectionally with user equipment therebyfurther reducing or minimizing a measure of interference. While thepresent invention has been described in detail by way of illustrationand example of preferred embodiments, numerous modifications,substitutions and/or alterations are possible without departing from thescope of the invention as described herein. Numerous combinations,sub-combinations, modifications, alterations and/or substitutions ofembodiments described herein will become apparent to those skilled inthe art. Such combinations, sub-combinations, modifications, alterationsand/or substitutions of the embodiments described herein may be used toform one or more additional embodiments without departing from the scopeof the present invention.

Embodiments of the present invention have been described above in termsof systems, methods, devices and/or computer program products thatprovide communication devoid of cyclostationary features. However, otherembodiments of the present invention may selectively providecommunications devoid of cyclostationary features. For example, as shownin FIG. 16, if LPI/LPD/LPE communications are desired, thennon-cyclostationary waveforms may be transmitted. In contrast, whenLPI/LPD/LPE communications need not be transmitted, cyclostationarywaveforms may be used. An indicator may be provided to allow a receiverto determine whether cyclostationary or non-cyclostationary waveformsare being transmitted. Accordingly, a given system, method, deviceand/or computer program can operate in one of two modes, depending uponwhether LPI/LPD/LPE communications are desired.

The present invention has been described with reference to blockdiagrams and/or flowchart illustrations of methods, apparatus (systems)and/or computer program products according to embodiments of theinvention. It is understood that a block of the block diagrams and/orflowchart illustrations, and combinations of blocks in the blockdiagrams and/or flowchart illustrations, can be implemented by computerprogram instructions. These computer program instructions may beprovided to a processor of a general purpose computer, special purposecomputer, and/or other programmable data processing apparatus to producea machine, such that the instructions, which execute via the processorof the computer and/or other programmable data processing apparatus,create means (functionality) and/or structure for implementing thefunctions/acts specified in the block diagrams and/or flowchart block orblocks.

These computer program instructions may also be stored in acomputer-readable memory that can direct a computer or otherprogrammable data processing apparatus to function in a particularmanner, such that the instructions stored in the computer-readablememory produce an article of manufacture including instructions whichimplement the function/act specified in the block diagrams and/orflowchart block or blocks.

The computer program instructions may also be loaded onto a computer orother programmable data processing apparatus to cause a series ofoperational steps to be performed on the computer or other programmableapparatus to produce a computer-implemented process such that theinstructions which execute on the computer or other programmableapparatus provide steps for implementing the functions/acts specified inthe block diagrams and/or flowchart block or blocks.

Accordingly, the present invention may be embodied in hardware and/or insoftware (including firmware, resident software, micro-code, etc.).Furthermore, the present invention may take the form of a computerprogram product on a computer-usable or computer-readable storage mediumhaving computer-usable or computer-readable program code embodied in themedium for use by or in connection with an instruction execution system.In the context of this document, a computer-usable or computer-readablemedium may be any medium that can contain, store, communicate,propagate, or transport the program for use by or in connection with theinstruction execution system, apparatus, or device.

It should also be noted that in some alternate implementations, thefunctions/acts noted in the blocks of the block diagrams/flowcharts mayoccur out of the order noted in the block diagram/flowcharts. Forexample, two blocks shown in succession may in fact be executedsubstantially concurrently or the blocks may sometimes be executed inthe reverse order, depending upon the functionality/acts involved.Moreover, the functionality of a given block of the flowcharts/blockdiagrams may be separated into multiple blocks and/or the functionalityof two or more blocks of the flowcharts/block diagrams may be at leastpartially integrated.

Next Generation (XG) Chipless Spread-Spectrum Communications (CSSC)

Introduction & Executive Summary:

According to some embodiments of a neXt Generation (XG) ChiplessSpread-Spectrum Communications (CSSC) system, described furtherhereinbelow and referred to as “XG-CSSC,” XG-CSSC provides extremeprivacy, cognitive radio capability, robustness to fading andinterference, communications performance associated with M-aryorthonormal signaling and high multiple-access capacity. XG-CSSC usesspread-spectrum waveforms that are devoid of chipping and devoid of anycyclostationary signature, statistically indistinguishable from thermalnoise and able to cognitively fit within any available frequency space(narrow-band, broad-band, contiguous, non-contiguous).

According to some embodiments, XG-CSSC maintains some or all desirablefeatures of classical direct-sequence spread-spectrum communicationswhile providing new dimensions that are important to military andcommercial systems. For military communications, XG-CSSC combines M-aryorthonormal signaling with chipless spread-spectrum waveforms to provideextreme covertness and privacy. Military wireless networks whose missionis to gather and disseminate intelligence stealthily, in accordance withLow Probability of Intercept (LPI), Low Probability of Detection (LPD)and Low Probability of Exploitation (LPE) doctrine, may use XG-CSSCterrestrially and/or via satellite. In situations where armed forcesface difficult spectrum access issues, XG-CSSC may be used tocognitively and covertly utilize spectrum resources at minimal impact toincumbent users.

Commercially, XG-CSSC may be used to provide opportunisticcommunications using spectrum that is detected unused. As spectrum usagecontinues to increase, it may become important to equip networks anduser devices with agility to use opportunistically any portion (orportions) of a broad range of frequencies that is/are detected as unusedor lightly used. A regime is envisioned wherein primary usage ofspectrum and secondary (opportunistic) usage of the same spectrumco-exist on a non-interference, or substantially non-interference,basis.

XG-CSSC Fundamentals:

In accordance with XG-CSSC, a Gram-Schmidt Orthonormalization (GSO)procedure, or any other orthonormalization or orthogonalizationprocedure, may be applied to a set of “seed” functions, to generate anorthonormal/orthogonal set of waveforms. According to some embodiments,the seed functions may be discrete-time functions, may be constructedpseudo-randomly in accordance with, for example, Gaussian statistics(that may be truncated Gaussian statistics) and in accordance with anydesired power spectral density characteristic that may be predeterminedand/or adaptively formed based on cognitive radio principles. The GSOoperation performed on the seed functions yields a set ofGaussian-distributed orthonormal waveforms. The set ofGaussian-distributed orthonormal waveforms may be used to define asignaling alphabet that may be used to map an information sequence intospread-spectrum waveforms without resorting to chipping of theinformation sequence.

Referring to FIG. 17, a Power Spectrum Estimator (PSE) may be used toidentify frequency content being radiated by other transmitters. Thismay be accomplished by, for example, subjecting a band of frequencies,over which it is desired to transmit information, to a Fast FourierTransform (FFT). Responsive to the output of the PSE, a “Water-FillingSpectrum Shape” (WFSS) may be formed in the FFT domain. Each element(bin) of the WFSS FFT may be assigned a pseudo-random phase value thatmay be chosen from (0, 2π). An Inverse Fast Fourier Transform (IFFT) maybe applied to the WFSS FFT, as illustrated in FIG. 1, to generate acorresponding Gaussian-distributed discrete-time function. (Thetechnique is not limited to Gaussian distributions. However, theGaussian distribution is of particular interest since waveforms thathave Gaussian statistics and are devoid of cyclostationary features aresubstantially indistinguishable from thermal noise.) The process may berepeated M times to produce a set of M independent Gaussian-distributeddiscrete-time functions. Still referring to FIG. 17, the output valuesof the IFFT may be limited in amplitude, in accordance with a truncatedGaussian distribution, in order to minimize non-linear distortioneffects in the amplification stages of the radio.

We let the set of M independent Gaussian-distributed discrete-timefunctions be denoted by {S(nT)}={S₁(nT), S₂(nT), . . . , S_(M)(nT)};n=1, 2, . . . , N. We also let a one-sided bandwidth of {S(nT)} belimited to B Hz. As such, a number of orthogonal waveforms that may begenerated from {S(nT)} may, in accordance with established theorems, beupper-bounded by 2.4πB; where τ=NT. (See P. M. Dollard, “On thetime-bandwidth concentration of signal functions forming given geometricvector configurations,” IEEE Transactions on Information Theory, IT-10,pp. 328-338, October 1964; also see H. J. Landau and H. O. Pollak,“Prolate spheroidal wave functions, Fourier analysis and uncertainty—Thedimension of the space of essentially time-and band-limited signals,”BSTJ, 41, pp. 1295-1336, July 1962) Accordingly, {S(nT)} may besubjected to a GSO in order to generate a set of M orthonormal waveforms{U(nT)}≡{U₁(nT), U₂(nT), . . . , U_(M)(nT)}; n=1, 2, . . . , N.

The set of orthonormal waveforms {U₁(nT), U₂(nT), . . . , U_(M)(nT)} maybe used to define an M-ary orthonormal Gaussian-distributed signalingalphabet whose elements may be used to map an M-ary information sequence{I_(k)}; I_(k) ε {I₁, I₂, . . . , I_(M)} into a spread-spectrum waveformsequence {U_(k)(nT)}. (The discrete-time index “k” relates to thesignaling interval whereas the discrete-time index “n” refers to thewaveform sampling interval. A signaling interval includes N waveformsampling intervals.)

Thus, in accordance with M-ary signaling, a block of L bits (2^(L)=M)may be associated with one element of {U₁(nT), U₂(nT), . . . ,U_(M)(nT)}. Alternatively, since the system comprises M orthogonalchannels (as defined by the M orthonormal waveforms) two or more of theorthonormal waveforms may be transmitted simultaneously. In thisconfiguration, each one of the transmitted orthonormal waveforms may bemodulated by either “+1” or “−1.”, to reflect a state of an associatedbit, thus conveying one bit of information. The following exampleillustrates a trade off between M-ary orthogonal signaling and binarysignaling.

As stated earlier, a number of orthogonal waveforms that may begenerated from a set of seed waveforms {S(nT)} is upper-bounded by2.4τB. Let us assume that each seed waveform is band-limited to B=500kHz (one-sided bandwidth) and that the signaling interval τ=NT is 1 ms.Thus, M≦2.4τB=2.4*(10⁻³)*(0.5*10⁶)=1200. Assuming that a number of 1024of orthonormal waveforms can be constructed, transmitting oneorthonormal waveform may relay 10 bits of information. Thus, the M-arysignaling approach may yield a data throughput of 10 kbps (since thesignaling interval is 1 ms). Turning now to the binary signalingapproach, each one of a plurality of orthonormal waveforms may bemodulated by either “+1” or “−1” and transmitted, conveying 1 bit ofinformation. If all 1024 orthonormal waveforms are used, the datathroughput may be 1024 bits per τ=10⁻³ seconds or, 1.024 Mbps. It isseen that the two approaches differ in data throughput by 20 dB but theyalso differ in E_(b)/N₀ performance. Since the M-ary signaling schemeconveys 10 bits of information per transmitted waveform, while thebinary signaling approach conveys one bit of information per transmittedwaveform, the M-ary signaling approach enjoys a 10 dB E_(b)/N₀ advantageover the binary signaling approach. (Assuming the probability of errorassociated with a channel symbol is kept the same for the two signalingschemes.) Thus, whereas the binary signaling scheme may be ideallysuited for high-capacity multiple-access military and/or commercialcommunications, the M-ary signaling scheme may be preferred for certainspecial operations situations that require extreme covertness and/orprivacy.

A receiver that is configured to receive information from thetransmitter of FIG. 17, may be equipped with sufficient information togenerate a matched filter bank corresponding to the M-ary signalingalphabet {U₁(nT), U₂(nT), . . . , U_(M)(nT)}. FIG. 18 illustrates keyfunctions of such a receiver. The receiver may further be optimized forfading channels by using “rake” principles. In some embodiments, thereceiver may be configured to detect lightly used or unused frequenciesand instruct one or more transmitters, via a control channel message, totransmit information over the detected lightly used or unusedfrequencies. This may be accomplished, in some embodiments of theinvention, by configuring the receiver to instruct the one or moretransmitters by transmitting frequency-occupancy information, via thecontrol channel, over a predetermined, known to the one or moretransmitters, frequency interval, that may contain interference. Thepredetermined frequency interval may, according to some embodiments, bechanging with time responsive to, for example, a Time-of-Day (ToD) valueand/or any other input. The frequency-occupancy information may be ofrelatively low data rate and the predetermined frequency interval may berelatively large in bandwidth so as to provide sufficient processinggain to overcome the interference. In further embodiments of theinvention, one or more elements of the M-ary signaling alphabet may beprecluded from being used for wireless transmission and this may be usedto provide a receiver with error detection and/or error correctioncapability, as will be appreciated by those skilled in the art.

Preliminary Computer Simulations:

Transmission and reception of information based on XG-CSSC waveforms hasbeen simulated using 16-ary Gaussian-distributed orthonormal alphabetsthat were constructed in accordance with the principles describedherein. FIG. 19( a) is a Power Spectral Density (“PSD”) of a transmittedXG-CSSC carrier in an interference-free environment (or in the presenceof interference but without the cognitive function having beenactivated). In contrast, FIG. 19( b) shows the impact of a radio'scognitive function. As seen from FIG. 19( b), responsive to a detectionof interference (indicated in FIG. 19( b) by the red or lighter trace),the PSD of a XG-CSSC carrier is “molded” around the interference. Thatis, the radio's cognitive function senses the power spectrumdistribution of interference and forms a 16-ary signaling alphabet withspectral content that avoids the interference. FIG. 19( c) shows the PSDof the XG-CSSC carrier (of FIG. 19( a) or 19(b)) following square-lawdetection, illustrating a featureless (non-cyclostationary) naturethereof. By comparison, the first and second traces of FIG. 20 show aPSD of conventional QPSK and a PSD of conventional QPSK followingsquare-law detection, illustrating a cyclostationary signature ofconventional QPSK.

FIG. 21 shows a constellation associated with transmission of 20,00016-ary symbols of the XG-CSSC carrier (of FIG. 3( a) or 3(b)) and FIG.22 represents a histogram thereof. It is seen from FIGS. 3, 5 and 6 thatXG-CSSC transmissions may be substantially featureless and substantiallyindistinguishable from thermal noise.

Communications performance has also been evaluated. FIG. 23 shows a BitError Rate (“BER”) vs. a Symbol Energy to Noise Power Spectral Density(“E_(s)/N₀”) for uncoded 16-ary XG-CSSC and uncoded spread-spectrum16-QAM. (See Donald L. Schilling et al. “Optimization of the ProcessingGain of an M-ary Direct Sequence Spread Spectrum Communication System,”IEEE Transactions on Communications, Vol. Com-28, No. 8, August 1980.)Spread-spectrum 16-QAM was chosen for this comparison in order to keep anumber of transmitted bits per symbol invariant between the twotransmission formats. The E_(s)/N₀ advantage of XG-CSSC is apparent,owing to its orthonormal signaling alphabet. It is seen that at 10⁻²BER, XG-CSSC enjoys almost a 5 dB advantage over 16-QAM.

FIG. 24 shows BER performance subject to Co-Channel (“CC”) interference.The two systems (16-ary XG-CSSC and spread-spectrum 16-QAM) remainuncoded as in FIG. 23. Two types of CC interference are considered:Wide-Band (“WB”) and Band-Pass (“BP”). The WB interference is modeled aswideband complex Gaussian noise and its PSD spans the entire desiredsignal spectrum. The BP interference is modeled as band-pass complexGaussian noise and its PSD spans only 20% of the desired signalspectrum. The power of interference (whether WB or BP) is made equal tothe power of the desired signal. In FIG. 24, the cognitive aspect ofXG-CSSC is not activated. As a consequence, the interference spectrumand the XG-CSSC spectrum remain co-channel impairing BER performance.

FIG. 25 focuses on the impact of BP interference and displays XG-CSSCsystem performance with and without cognition. The two systems remainuncoded, as above, and the power of interference remains equal to thepower of the desired signal. In the legend of FIG. 25, the term“Adaptive XG-CSSC” indicates that the associated curve representsXG-CSSC with the cognitive feature active. It can be observed thatperformance of XG-CSSC subject to the cognitive feature (interferenceavoidance) is indistinguishable from the interference-free case (theblue [square points] and green [star points] curves are on top of eachother).

Embodiments of the present invention have been described above in termsof systems, methods, devices and/or computer program products thatprovide communication devoid of cyclostationary features. However, otherembodiments of the present invention may selectively providecommunications devoid of cyclostationary features. For example, as shownin FIG. 16 if LPI/LPD/LPE communications are desired, thennon-cyclostationary waveforms may be transmitted. In contrast, whenLPI/LPD/LPE communications need not be transmitted, cyclostationarywaveforms may be used. An indicator may be provided to allow a receiverto determine whether cyclostationary or non-cyclostationary waveformsare being transmitted. Accordingly, a given system, method, deviceand/or computer program can operate in one of two modes, depending uponwhether LPI/LPD/LPE communications are desired.

The present invention has been described with reference to blockdiagrams and/or flowchart illustrations of methods, apparatus (systems)and/or computer program products according to embodiments of theinvention. It is understood that a block of the block diagrams and/orflowchart illustrations, and combinations of blocks in the blockdiagrams and/or flowchart illustrations, can be implemented by computerprogram instructions. These computer program instructions may beprovided to a processor of a general purpose computer, special purposecomputer, and/or other programmable data processing apparatus to producea machine, such that the instructions, which execute via the processorof the computer and/or other programmable data processing apparatus,create means (functionality) and/or structure for implementing thefunctions/acts specified in the block diagrams and/or flowchart block orblocks.

These computer program instructions may also be stored in acomputer-readable memory that can direct a computer or otherprogrammable data processing apparatus to function in a particularmanner, such that the instructions stored in the computer-readablememory produce an article of manufacture including instructions whichimplement the function/act specified in the block diagrams and/orflowchart block or blocks.

The computer program instructions may also be loaded onto a computer orother programmable data processing apparatus to cause a series ofoperational steps to be performed on the computer or other programmableapparatus to produce a computer-implemented process such that theinstructions which execute on the computer or other programmableapparatus provide steps for implementing the functions/acts specified inthe block diagrams and/or flowchart block or blocks.

Accordingly, the present invention may be embodied in hardware and/or insoftware (including firmware, resident software, micro-code, etc.).Furthermore, the present invention may take the form of a computerprogram product on a computer-usable or computer-readable storage mediumhaving computer-usable or computer-readable program code embodied in themedium for use by or in connection with an instruction execution system.In the context of this document, a computer-usable or computer-readablemedium may be any medium that can contain, store, communicate,propagate, or transport the program for use by or in connection with theinstruction execution system, apparatus, or device.

It should also be noted that in some alternate implementations, thefunctions/acts noted in the blocks of the block diagrams/flowcharts mayoccur out of the order noted in the block diagram/flowcharts. Forexample, two blocks shown in succession may in fact be executedsubstantially concurrently or the blocks may sometimes be executed inthe reverse order, depending upon the functionality/acts involved.Moreover, the functionality of a given block of the flowcharts/blockdiagrams may be separated into multiple blocks and/or the functionalityof two or more blocks of the flowcharts/block diagrams may be at leastpartially integrated.

In the specification and the Figures thereof, there have been disclosedembodiments of the invention and, although specific terms are employed,they are used in a generic and descriptive sense only and not forpurposes of limitation; the scope of the invention being set forth inthe following claims.

1. A communications method comprising: providing a frequency content byFourier transforming a signal; then forming at baseband a desiredspectrum shape that differs from the frequency content, responsive tothe frequency content; then generating at baseband a waveform by inverseFourier transforming the desired spectrum shape; and then transmittingthe waveform by using a plurality of elements thereof, sequentially oneafter another, to modulate a single carrier frequency; whereingenerating at baseband a waveform by inverse Fourier transforming thedesired spectrum shape comprises: generating at baseband a discretetime-domain waveform U(nT) without resorting to chipping of the inverseFourier transform of the desired spectrum shape with a binary waveform;wherein n denotes a discrete time index of U(nT), wherein n=1, 2, . . ., N; and NT≦τ; wherein τdenotes a time span of the discrete time-domainwaveform U(nT); and wherein T>0; and wherein transmitting the waveformby using a plurality of elements thereof, sequentially one afteranother, to modulate a single carrier frequency comprises: usingsubstantially all of the elements of U(nT) sequentially to modulate thesingle carrier frequency by using U(T), followed by using U(2T), . . . ,followed by using U(NT).
 2. The communications method according to claim1, wherein said forming at baseband a desired spectrum shape isperformed at a transmitter.
 3. The communications method according toclaim 1, wherein said forming at baseband a desired spectrum shape isperformed at a distance from a transmitter and is then relayed to thetransmitter.
 4. The communications method according to claim 1, whereinsaid forming at baseband a desired spectrum shape comprises: using afirst plurality of frequencies over a first time interval to form atbaseband a first desired spectrum shape and then, using the firstdesired spectrum shape and without resorting to chipping with a binarywaveform, to generate at baseband a first waveform; and using a secondplurality of frequencies over a second time interval to form at basebanda second desired spectrum shape and then, using the second desiredspectrum shape and without resorting to chipping with a binary waveform,to generate at baseband a second waveform; wherein the first pluralityof frequencies differs from the second plurality of frequencies in atleast one frequency; and wherein the first and second desired spectrumshapes differ therebetween.
 5. The communications method according toclaim 4, wherein the first waveform comprises a first time duration andwherein the second waveform comprises a second time duration thatdiffers from the first time duration.
 6. The communications methodaccording to claim 1, wherein said generating at baseband a waveform byinverse Fourier transforming the desired spectrum share furthercomprises: generating at baseband first and second waveforms comprisingrespective first and second time durations that differ therebetween. 7.The communications method according to claim 1, wherein said forming atbaseband a desired spectrum shape comprises: forming the desiredspectrum shape to include a first frequency set comprising a firstspectral level that is non-zero and to also include a second frequencyset comprising a second spectral level that is also non-zero.
 8. Thecommunications method according to claim 7, further comprising:separating the first and second frequency sets by a third frequency setcomprising a spectral level that is substantially zero.
 9. Thecommunications method according to claim 1, wherein said generating atbaseband a waveform further comprises: processing so that a maximumamplitude value at an output of the inverse Fourier transform be limitedin order to reduce non-linear distortion effects in an amplificationstage of a transmitter.
 10. The communications method according to claim1, wherein said waveform comprises first and second waveforms at leastone of which is generated pseudo-randomly and independently of aninformation symbol sequence that is to be transmitted/received,responsive to a predetermined statistical distribution.
 11. Thecommunications method according to claim 10, wherein the predeterminedstatistical distribution comprises a Gaussian distribution.
 12. Thecommunications method according to claim 1, wherein the waveform isdevoid of a regularly repeating peak amplitude level during saidtransmitting.
 13. The communications method according to claim 10,wherein each one of the first and second waveforms comprises a waveformthat is generated pseudo-randomly and independently of the informationsymbol sequence that is to be transmitted/received; and wherein thefirst and second waveforms comprise a statistical independence and anorthogonality therebetween.
 14. A communications method comprising:providing a frequency content by Fourier transforming a signal; thenforming at baseband a desired spectrum shape that differs from thefrequency content, responsive to the frequency content; then generatingat baseband a waveform by inverse Fourier transforming the desiredspectrum shape and without resorting to chipping of the inverse Fouriertransform of the desired spectrum shape with a binary waveform; and thentransmitting the waveform by using a plurality of elements thereof,sequentially one after another, to modulate a single carrier frequency;wherein forming at baseband a desired spectrum shape comprises:selecting a frequency interval over which the waveform is to exist;allowing at least one frequency that is included in the selectedfrequency interval to provide a frequency content to the waveform; andexcluding at least one frequency that is included in the selectedfrequency interval from providing a frequency content to the waveform.15. The communications method according to claim 14, wherein saidforming at baseband a desired spectrum shape is performed at atransmitter.
 16. The communications method according to claim 14,wherein said forming at baseband a desired spectrum shape is performedat a distance from a transmitter and is then relayed to the transmitter.17. The communications method according to claim 14, wherein saidforming at baseband a desired spectrum shape comprises: using a firstplurality of frequencies over a first time interval to form at basebanda first desired spectrum shape and then, using the first desiredspectrum shape and without resorting to chipping with a binary waveform,to generate at baseband a first waveform; and using a second pluralityof frequencies over a second time interval to form at baseband a seconddesired spectrum shape and then, using the second desired spectrum shapeand without resorting to chipping with a binary waveform, to generate atbaseband a second waveform; wherein the first plurality of frequenciesdiffers from the second plurality of frequencies in at least onefrequency and wherein the first and second desired spectrum shapesdiffer therebetween.
 18. The communications method according to claim17, wherein the first waveform comprises a first time duration andwherein the second waveform comprises a second time duration thatdiffers from the first time duration.
 19. The communications methodaccording to claim 14, wherein said generating at baseband a waveform byinverse Fourier transforming the desired spectrum shape comprises:generating at baseband first and second waveforms comprising respectivefirst and second time durations that differ therebetween.
 20. Thecommunications method according to claim 14, wherein said forming atbaseband a desired spectrum shape comprises: forming the desiredspectrum shape to include a first frequency set comprising a firstspectral level that is non-zero and to also include a second frequencyset comprising a second spectral level that is also non-zero.
 21. Thecommunications method according to claim 20, further comprising:separating the first and second frequency sets by a third frequency setcomprising a spectral level that is substantially zero.
 22. Thecommunications method according to claim 14, wherein said generating atbaseband a waveform comprises: processing so that a maximum amplitudevalue at an output of the inverse Fourier transform be limited in orderto reduce non-linear distortion effects in an amplification stage of atransmitter.
 23. The communications method according to claim 14,wherein the waveform comprises first and second waveforms at least oneof which is generated pseudo-randomly and independently of aninformation symbol sequence that is to be transmitted/received,responsive to a predetermined statistical distribution.
 24. Thecommunications method according to claim 23, wherein the predeterminedstatistical distribution comprises a Gaussian distribution.
 25. Thecommunications method according to claim 14, wherein the waveform isdevoid of a regularly repeating peak amplitude level during saidtransmitting.
 26. The communications method according to claim 23,wherein each one of the first and second waveforms comprises a waveformthat is generated pseudo-randomly and independently of the informationsymbol sequence that is to be transmitted/received; and wherein thefirst and second waveforms comprise a statistical independence and anorthogonality therebetween.
 27. A communications system comprising; aprocessor that is configured to provide a frequency content by Fouriertransforming a signal; to form at baseband a desired spectrum shape thatdiffers from the frequency content, responsive to the frequency contentand to generate at baseband a waveform by inverse Fourier transformingthe desired spectrum shape without resorting to chipping of the inverseFourier transform of the desired spectrum shape with a binary waveform;and a transmitter that is configured to transmit the waveform,comprising a plurality of elements, by using the plurality of elements,sequentially one after another, to modulate a single carrier frequency;wherein the waveform comprises a discrete time-domain waveform U(nT);wherein n denotes a discrete time index of U(nT), wherein n=1, 2, . . ., N; and NT≦τ; wherein τ denotes a time span of the discrete time-domainwaveform U(nT); and wherein T>0; and wherein the transmitter is furtherconfigured to use substantially all of the elements of U(nT)sequentially to modulate the single carrier frequency by using U(T),followed by using U(2T), . . . , followed by using U(NT).
 28. Thecommunications system according to claim 27, wherein the processor issubstantially co-located with the transmitter.
 29. The communicationssystem according to claim 27, wherein the processor is at a distancefrom the transmitter.
 30. The communications system according to claim27, wherein said desired spectrum shape comprises first and seconddesired spectrum shapes over respective first and second time intervalsand wherein the first desired spectrum shape comprises: a firstplurality of frequencies that is used to generate at baseband a firstwaveform without resorting to chipping with a binary waveform; andwherein the second desired spectrum shape comprises: a second pluralityof frequencies that is used to generate at baseband a second waveform,without resorting to chipping with a binary waveform; wherein the firstplurality of frequencies differs from the second plurality offrequencies in at least one frequency and wherein the first and seconddesired spectrum shapes differ therebetween.
 31. The communicationssystem according to claim 30, wherein the first waveform comprises afirst time duration and wherein the second waveform comprises a secondtime duration that differs from the first time duration.
 32. Thecommunications system according to claim 27, wherein the waveformfurther comprises first and second waveforms comprising respective firstand second time durations that differ therebetween.
 33. Thecommunications system according to claim 27, wherein said desiredspectrum shape includes a first frequency set comprising a firstspectral level that is non-zero and also includes a second frequency setcomprising a second spectral level that is also non-zero.
 34. Thecommunications system according to claim 33, wherein the processorand/or the transmitter is/are configured to: separate the first andsecond frequency sets by a third frequency set comprising a spectrallevel that is substantially zero.
 35. The communications systemaccording to claim 27, wherein the processor is further configured tofunction so that a maximum amplitude value at an output of the inverseFourier transform be limited in order to reduce non-linear distortioneffects in an amplification stage of the transmitter.
 36. Thecommunications system according to claim 27, wherein the waveformcomprises first and second waveforms at least one of which is generatedpseudo-randomly and independently of an information symbol sequence thatis to be transmitted/received, responsive to a predetermined statisticaldistribution.
 37. The communications system according to claim 36,wherein the predetermined statistical distribution comprises a Gaussiandistribution.
 38. The communications system according to claim 27,wherein the waveform is devoid of a regularly repeating peak amplitudelevel while the waveform is being transmitted by the transmitter. 39.The communications system according to claim 36, wherein each one of thetint and second waveforms comprises a waveform that is generatedpseudo-randomly and independently of the information symbol sequencethat is to be transmitted/received; and wherein the first and secondwaveforms comprise a statistical independence and an orthogonalitytherebetween.
 40. A communications system comprising: a processor thatis configured to provide a frequency content by Fourier transforming asignal; to form at baseband a desired spectrum shape that differs fromthe frequency content, responsive to the frequency content and togenerate at baseband a waveform by inverse Fourier transforming thedesired spectrum shape without resorting to chipping of the inverseFourier transform of the desired spectrum shape with a binary waveform;and a transmitter that is configured to transmit the waveform,comprising a plurality of elements, by using the plurality of elements,sequentially one after another, to modulate a single carrier frequency;wherein the processor is further configured to: select a frequencyinterval over which the waveform is to exist; allow at least onefrequency that is included in the selected frequency interval to providea frequency content to the waveform; and exclude at least one frequencythat is included in the selected frequency interval from providing afrequency content to the waveform.
 41. The communications systemaccording to claim 40, wherein the processor is further configured touse the frequency interval that is selected over a first time intervaland then to change the frequency interval that is selected and to usethe changed frequency interval over a second time interval.
 42. Thecommunications system according to claim 40, wherein the processor andthe transmitter are substantially co-located therebetween.
 43. Thecommunications system according to claim 40, wherein the processor islocated a distance from the transmitter.
 44. The communications systemaccording to claim 40, wherein said desired spectrum shape comprisesfirst and second desired spectrum shapes over respective first andsecond time intervals and wherein the first desired spectrum shapecomprises: a first plurality of frequencies that is used to generate atbaseband a first waveform without resorting to chipping with a binarywaveform; and wherein the second desired spectrum shape comprises: asecond plurality of frequencies that is used to generate at baseband asecond waveform without resorting to chipping with a binary waveform;wherein the first plurality of frequencies differs from the secondplurality of frequencies in at least one frequency and wherein the firstand second desired spectrum shapes differ therebetween.
 45. Thecommunications system according to claim 44, wherein the first waveformcomprises a first time duration and wherein the second waveformcomprises a second time duration that differs from the first timeduration.
 46. The communications system according to claim 40, whereinthe waveform further comprises first and second waveforms comprisingrespective first and second time durations that differ therebetween. 47.The communications system according to claim 40, wherein said desiredspectrum shape includes a first frequency set comprising a firstspectral level that is non-zero and also includes a second frequency setcomprising a second spectral level that is also non-zero.
 48. Thecommunications system according to claim 47, wherein the processorand/or the transmitter is/are configured to: separate the first andsecond frequency sets by a third frequency set comprising a spectrallevel that is substantially zero.
 49. The communications systemaccording to claim 40, wherein the processor is further configured tofunction so that a maximum amplitude value at an output of the inverseFourier transform be limited in order to reduce non-linear distortioneffects in an amplification stage of the transmitter.
 50. Thecommunications system according to claim 40, wherein the waveformcomprises first and second waveforms at least one of which is generatedpseudo-randomly and independently of an information symbol sequence thatis to be transmitted/received, responsive to a predetermined statisticaldistribution.
 51. The communications system according to claim 50,wherein the predetermined statistical distribution comprises a Gaussiandistribution.
 52. The communications system according to claim 40,wherein the waveform is devoid of a regularly repeating peak amplitudelevel while the waveform is being transmitted by the transmitter. 53.The communications system according to claim 50, wherein each one of thefirst and second waveforms comprises a waveform that is generatedpseudo-randomly and independently of the information symbol sequencethat is to be transmitted/received; and wherein the first and secondwaveforms comprise a statistical independence and an orthogonalitytherebetween.